The other thing about homebrew is that, well, a lot of it isn't easily searchable and viewable online. It exists in people's binders and scrawled across thousands of pieces of graph paper the world over.
Anecdotally, I can say that homebrewed settings are more popular in my neck of the woods than games in published settings, some of them quite weird! But people tend not to publish them online because that takes TONS of effort, and most DMs fall into 1 of 2 categories: 1)they want to use a published setting because it saves a lot of effort, and because it often comes with pre-existing player buy-in or 2) they want to homebrew their own custom setting themselves. As a result of that, you get a lot more classes, monsters, and adventures put online than whole campaign settings.
All that said, as far as official WotC stuff I totally see why people feel that the 70's and 80's had more officially supported experimentation than today. When was the last time WotC published a brand new campaign setting? At least, one that wasn't just a product tie-in for an existing IP (sorry Ravnica!)? WotC has been so careful about curating its existing, profitable campaign worlds that I sort of feel like they've completely avoided doing anything risky and new for a long time now.
Still love 5E, since I'm gonna run a homebrew setting either way 90% of the time. But I get it.