Most of the patreon pages I've seen where people are bringing in that sort of money it's not a single dev but a team. $10-20k per month for 1 person is enough to quit your job and do full time, but if you spread that out over even a 2 person team then you could probably make more at your "real job" unless you live in a low wage country where $5k or so is a lot of money. I couldn't even cover my mortgage with that. So I would guess most devs are only doing it part time unless they hate their "real job" so much that they're willing to take a big pay cut.
I can definitely see it still having an influence on the quality of the game though. If I'm a part time dev making a game as a hobby and only making $500 a month on Patreon, that's probably not even enough for me to be willing to spend money upgrading my computer and buying a bunch of art assets. (I might do it anyway but not because of the Patreon money). If I'm making $5k per month on Patreon, that's not enough for me to quit my day job and do it full time, but I could see buying a dedicated rendering machine and some art assets.
Now if you're bringing in say $30-40k per month and producing 3 or 4 games at the same time with a dedicated artist, dedicated writer, dedicated coder working full time, then that's a different story but I haven't seen many sites where it looks like anyone's got the kind of resources they'd need for that. Plus if you have a team with the skills/dedication for that, wouldn't you make more if you go work for Rockstar games or something? Or is it only the owners making serious money there? I have no idea.
There may be some teams with their own paywalled site not relying on Patreon that have those sorts of numbers, but I don't have any way to see stats on those.
