I do not remember what it was like back in the days of the RPGA, but in recent years, with Pathfinder Society and Adventurer's League only allowing their company's material, and many players maybe only getting to play through these organizations, that kind of mindset can stick with these players and DMs when they get to finally have a non-Organized Play game.
That's possibly part of the issue. But OP was always a thing, and always was official only. We're more aware of it, but I'm not certain *that* many more people are playing organized play.
I think three things had the strongest impact on homebrew:
1) The rise of official 3rd Party stuff during 3e
2) The wealth of official options during 3e
3 The rise of "balance"
Balance was the big one. Suddenly, things were either balanced or unbalanced and it was much more obvious what was good homebrew vs bad. Prior to 3e there was some element of "balance" but it was much more fluid. Designing
good homebrew was harder.
This is paired with all the 3PP, which really introduced many people to bad products. The idea that there wasn't some minimum standard of quality and you couldn't necessarily trust a product to be good.
Added into this drama was the myriad of options which made it less necessary to homebrew. If you wanted to play certain things in 2e you simply had to homebrew. You didn't in 3e: you just needed to find the right book. And it was a simple matter to find options you wanted to play: it was easier to base a character around the options available than find options that fit the character.
The internet and even piracy likely made a difference as well. If you wanted an option in 1e or 2e and didn't have the book, finding out where that option would be could be tricky, and getting a copy of that exact book was hard. Then it was a Google search or eBay/Amazon purchase away. You were more aware of what options were out there.
And even if you didn't want to buy the book, it was possible to get the options through a PDF. Not having an unlimited gaming budget was less of an obstacle. It was easily to track down an illegal copy of a warrior prestige class than it was to design your own...
Spinning out of that, I think a lot of DMs pushed back against the options. Because there was so much power creep in the game, it became desirable to get "back to basics" and focus on just the core rulebooks. I saw several DMs doing a PHB only campaign, with even official material requiring a stamp of approval.