The main reason is that there isn't really a big market for small sets. If you go on a trip you can bring a phone or handheld game system and get the same effect. Also the constant scare of small parts over decades makes it hard to market to families with younger children.
I'd have to agree the main point is the toy companies just phone it in and don't actually put in effort anymore. Like >>7537255
points out. Their new attempts are so half-ass it doesn't hook kids and fails at a nostalgia for older collectors. No one really wants that crap.
Part of me also wants to blame the lack of good tie-ins and licencing fees for proven IPs in the market are out of hand. You used to be able to make a TV show and market anything, but that no longer works. And so the good IPs are all held hostage with higher fees.
It's just not worth the risk to toy companies anymore.
I think the last point would be that these used to be the budget playset idea. Playsets are kind of a dead thing on their own so a budget option no longer makes sense.>>7538210
I know older ones did stickers a lot, kind of how that turtle uses them. That's not really as bit an issue so much as everything's so flat in the new one you posted. The stuff that folds out are flat, the background lacks texture, etc. It comes across as cheap and boring, even though the figures are probably a huge step up. It's not inviting to play with and no details that wow a kid when they're playing and notice something.