Creating your own thing was not just a Critical Role thing, that was ALWAYS the main thing with D&D and was always born out by data collected by TSR and WOTC. Homebrew was always the majority of games going back to 0e. The SPlat books, edition neutral materials outsold setting materials, with only FR really coming close to being an official setting and almost getting the axe in the 3e era and being shifted towards being crunchy to the detriment of fluffy.
TSR cranked out setting materials in 2e and lost money on them, as well documented by Ryan Dancey when he was the brand manager back in the 3e days talking about what WOTC found look at the TSR finances, and why they retracted to just supporting FR. Sales were there to support FR from licensing and sourcebook sales. They cancelled all the other settings and only supported one other setting in the 3.x era, in the form of Eberron. The rest were licensed to other companies like WHite Wolf with Ravenloft and Gamma World and Margaret Weis with Dragonlance with WOTC publishing the core DL sourcebook.
4e saw setting books get retracted to a Player's Guide, a DM's Guide and an Adventure with FR being revisited for Neverwinter to support the video game. And then they only published FR, Eberron and Dark Sun with plans scuppered for a standalone Ravenloft game and a Nentir Vale gazeteer.
D&D, more than any RPG, has ALWAYS been about homebrew and DIY. The best supplements in the 2e era were DIY materials like the Castles & Catacombs guides and the Historical reference books. Traveller is probably the only game that could rival D&D on that and also the only game that could rival D&D on that canon arguments as well. One could be misled by the love people have for the settings and canon arguments but Critical Role, and I love Critical Role, I am a die hard Critical Role fan, has little to do with the "make it yourself" movement in D&D. D&D has barely supported a setting in much of any capacity in 14 years. You can count the support for FR without running out of fingers beyond some adventures.
Dude, I've been playing for the better part of 30 years. My title on this forum is "Creator of Worlds". You don't need to tell me that D&D encouraged people to create their own worlds 20+ years ago. You also don't need to walk me through D&D's history of Campaign settings.
The point is that Critical Role, with it's massive audience and influence, said "Don't just play in our world, create your own" to people who weren't playing 5 years ago. To people who weren't playing 1 year ago.
Critical Role became a popular property and then expressly said "Do your own thing, don't copy what we're doing" and brand spanking new players dove into that, is the point I'm making. When it would've been vastly easier and more profitable to instead release splat after splat tied to Exandria and the Critical Role characters, which their audience would've eagerly consumed with neither hesitation nor qualm, because that's how our current media consumption works, they actively told people to go out and make their own worlds.
Like... seriously. I'm in Twitch Streamer Discords and when I showed some of them Sins of the Scorpion Age they were -confused-. Shocked at how much stuff I just "Made Up" even though a bunch of them are D&D players, themselves. Even now, in Ficus Fox's discord there's this perception that a team of people, of whom I was just one, put the world together... because it's seen as too much.
Here's some Excerpts from one conversation I had, there, a month ago and a few notes when I released the Discord link.
TLR:
"Kids, Today" would probably have just bought everything Exandria if they'd been given the chance. Instead, Mercer and Crew actively encouraged them to create their own worlds. And we're talking about a Fanbase that gave them almost $12 million to make a cartoon about their characters...
The idea that what TSR encouraged 40 years ago means more than a fart on a windy day in our current consumer culture is just wild...