It's always been that way. The belief must be there's no money in trying to start Trek fans off young.
The Trek 8" Mego figures of the 70s coincided with Filmation's TAS in the 70s. Saturday morning TV. TOS reuns were in early-evening syndicated rotation, stripped five-nights-per week. (ie. Kids' viewing.)
Playmates' TNG figures (in 5" and 9" sizes) in the late 80s/early 90s were quite dominant in the toy aisles of the day. TNG was airing in prime time, first-run syndication. (ie. Kids' viewing.)
1996 was a fairly big TOS anniversary celebration for merchandise.
Once DS9, VGR and ENT started airing in later and later timeslots, the kids and families watching together began to fall away.
I'd suggest this: Star Trek does not have an inclusive fan base. We're not fun to be around, we're generally miserable about everything in the franchise, we're not welcoming, and (in many cases) we're just downright mean-spirited to each other, the PTB, and especially to newbies. Why would anyone be excited to jump on that train?
After discovering TMP in 1979, some of my first research included the books "World of Star Trek", "Star Trek Lives!" and "The Making of the Trek Conventions", plus Susan Sackett's, David Gerrold's and Bjo Trimble's columns in "Starlog". These provided compelling evidence that fan gatherings were inclusive and fun... and they were! With a few provisos. Like all social clubs, there were still cliques and in-crowds, but overall, way more accepting than many other groups. IDIC was actually practised.
Star Trek isn't going to be driven forward by casual audiences. It will be driven by engaging a new and younger fanbase. Casual audiences don't give a shit and probably never will...
It was interesting when TNG was at its peak. Many members of the general public would identify themselves as Trek fans, but most were ready to move on to the next new, shiny thing when TNG ended its TV run. Keep in mind that, about the same time as TNG's US popularity, "Doctor Who" went into a long hiatus. Our Australian Trek club got overrun with brand new TNG fans (many despondent DW fans looking for a SF media fix) who had no inclination to find out about TOS. The UK magazine, "Doctor Who Bulletin" became "DWB", then "Dream Watch Bulletin", with the same old logo lettering but gradually full of TNG content.
... the existing fanbase is too fractured and too miserable to be a viable source of sustainability.
There are certainly some very negative fans out there these days. But we often forget that TAS, TMP, ST II, ST IV ("the dumbing down of Star Trek for the masses") and TNG all had their very loud detractors in their day. Some eventually relented, but many wandered away from Trek forever. I still like to look at each new Trek through my IDIC glasses. And I'm usually quite content.