I think the trend to go with Kirk and Spock comes more from the new movies and retailers assuming that fans want Kirk and Spock because those characters are back in the public consciousness.
When perhaps fans who do or would collect do want Picard and Co more?
I really think that "Kirk and Spock Hell" is actually the result of outdated views on the Trek toyline and on Trek as a whole. Back when Art Asylum first picked up the Trek license, TWOK was just turning 20, ENT was new, and we'd just seen the Playmates line crash and burn. While a lot of people wanted Art Asylum to just pick up where Playmates left off in the original 4.5" scale, starting with the ENT crew and then maybe doing updated versions of classic figures with a bit more articulation, Art Asylum wanted 7" figures, which in the long run seemed like a good call; they were a little larger, but had loads of extra detail to them. At the time, there was a good contingent of collectors who wanted more VOY stuff, especially stuff that Playmates never got too, and that wanted it while the show was still fresh in everyone's minds. This might have happened if NEM hadn't tanked and left figures warming shelves, and if ENT hadn't tanked doing the same thing and causing Art Asylum to make massive cuts to the line as a whole. When Art Asylum finally moved on from ENT, Trek was coming up on its 40th anniversary, and there was a huge demand for TOS merchandise, both for the 40th anniversary, and because logically, ENT toys should be followed by TOS toys, and then TNG, DS9, VOY toys just by going in order of the timeline. TOS had kind of been on the way backburner for several years, so there was an appetite for it both in toy form and in media form. George Takei was pitching his Captain Sulu concept, and realistically, Paramount should have green–lighted it as the timing was ideal for such a concept, and it easily would have made up for the faults with ENT. At the same time, Paramount was looking into several ideas for the movies. Some involved post–ENT stories set before Kirk's time, but Paramount decided against these because they were afraid to introduce a new cast on the big screen. Other ideas involved bringing a mixture of TNG/DS9/VOY characters to the big screen, but the idea that Paramount ultimately settled on was a pseudo–reboot, because the fad of rebooting movies and TV shows was really starting to take off, (blech,) and it was the easiest way to do a new TOS movie that was going to need a new cast anyway.
Naturally, Kirk and Spock likely sold because at the time, there weren't a whole lot of Kirk and Spock figures in a modern style, and with a new Kirk and a new Spock on the way, the focus was on the TOS characters. Now jump ahead ten years to today where we've got Kirk and Spock figures that have multiplied like Tribbles, an alternate continuity that's been criticized as "Trek–like substance" rather than actual Trek as the only new material in the franchise, and TOS nostalgia that's been milked to death at the cost of ignoring TNG–VOY. TNG turned 20 in 2007 and saw some acknowledgement, but by 2012, it's 25th anniversary went largely ignored with Into Darkness sucking up any promotional efforts for the series. (To CBS's credit, we did get TNG–R on Blu–Ray, but only on Blu–Ray, not on TV or any other format, and before most people had a Blu–Ray player.) Likewise, the aforementioned film's delay into 2013 subsequently ensured that DS9's 20th anniversary would pass unnoticed as well. VOY turned 20 last year and was also barely acknowledged, and now that it's been a good 15 years since 24th Century Trek has dominated anything, there's a demand for stuff from that era again, and a demand for a continuation from that point in the Prime Universe timeline, especially with Trek XI effectively shaking it up with the destruction of Romulus. DS9 and VOY toys are scarce, and even modern TNG figures still require a trip to eBay. People like me who grew up on TNG–VOY wanted TOS stuff a decade ago because we missed it the first time around, and wanted to expand beyond a massive gap in our collection, and now that expansion is largely complete. On the other hand, we now have huge gaps in comparable TNG–VOY merchandise, so there's demand for toys from that era. When I started collecting Art Asylum and subsequently DST's toys, nobody had done an Enterprise–A before, (the South Bend Enterprise was a refit, but not the "A," and was way before my time,) I didn't have a TOS phaser or tricorder, (my brother beat me to the Playmates version,) and I was thrilled when I finally got them. Today I have multiple TOS phasers, TOS tricorders, Enterprise–A's, TWOK and TOS 1701's, etc., but could use more TNG phasers and tricorders, a U.S.S. Voyager that's in line with my DST ship collection, and other items from TNG–VOY. I've got plenty of Kirks and Spocks to choose from though, and if I have to play in the TOS timeline only, I'd much rather have more McCoy's, Sulu's, and Scotty's than Kirk's and Spocks, altough I'd much rather set TOS aside for awhile. If DST gets a JJ–verse license though, that would be another story as those are fundamentally different Kirk's and Spocks than any that I have. (Oh and no disrespect meant to Chekov and Uhura; it's just that McCoy, Sulu, and Scotty had a lot more screen time that would make for interesting action figure possibilities.)
There is hope for TNG–VOY fans though as I'm starting to see at least TNG merchandise making its way back to shelves, most likely because of its impending 30th anniversary next year. Not long ago, I saw something on Amazon, something I've wanted since I was a kid: A TNG lunch box. It's metal, a nice step above the plastic lunchbox I'd carry as a kid, and it has the Enterprise–D embossed on it and looks completely awesome. Do I need a lunchbox? No. Will I likely buy this one as soon as I have some spare change? HELL YES! If nothing else I can display it with my other Trek stuff, or even use it to store something Trek related. As a kid I could never find a TNG lunchbox, but I still had one. My mother bought some random lunchbox (I think it had a Marvel character or something on it,) peeled the design on the front off, bought me some TNG stickers and then grabbed another package of them and used it to create a TNG lunchbox. To protect the stickers, a sheet of laminating paper was placed over where the stickers were and the previous design had been, and cut to fit the lunchbox. Voila, now I had a TNG lunchbox. Today, my one–of–a–kind TNG lunchbox now sits under my bed, holding an armada of "Star Trek" (and possibly some "Star Wars") Micro Machines, in and of themselves a product I wish Hasbro had revived when they had a Trek license, and wish they would revive if they still have said license. (They did it for "Star Wars," and they got my money, and I'd be even more excited if they did it for Trek.)
Of course, Trek merchandise of the TNG–VOY variety as a whole could still be a bit easier to get a hold of. While ThinkGeek has a new TNG beach towel, (you can pry the one I've been using since '92 from my cold, dead hands, along with the one I have that's identical but has never been used,) nobody seems to have a license to make Star Trek sheets for my bed, which is something that's irked me for years. I can find "Star Wars" sheets rather easily, and right before Lucasfilm was sold to Disney, there was even a set aimed primarily at adults, but something like Star Trek sheets with TNG or VOY "Delta Shield" communicators on them or starship blueprints are completely nonexistant. I may have to pay a small fortune for VOY toys, but at least they exist. If I want TNG–VOY bedding, or even TOS or ENT bedding, I'm completely out of luck.
As for the toys, most of the people I know would easily go for TNG–VOY over other forms of Trek. My first introduction to Trek was TNG, but I got into it at a much younger age than most of my friends. When my friends got into it, they did so largely through VOY, because at the time VOY premiered, they were in the 10–15 age range, while I was into TNG in some capacity while still in the single–digit age range. VOY and parts of DS9 were probably the first Trek series that I could completely comprehend the first time that I watched them though, and VOY and TNG constantly battle for the postion of being my favorite Trek series, and as a result, I tend to be most interested in toys from those two shows as well as from DS9. This doesn't mean that there isn't TOS stuff that I want, (there definitely is, and I've bought quite a few TOS toys already,) it's just that I'd prefer more from TNG–VOY, and as much as ENT as a series irks me, I'd easily plunk down the cash for an NX–02 Columbia, or an NX–09 I.S.S. Avenger today if given the opportunity.