For me it somehow feels like my donations are being received in a more meaningful way via Patreon than anywhere else, even if the creator has no rewards set up. Like, a "Donate" button on a creator's website just feels like sending my money into a black hole. But sending it in Patreon makes me feel like a real supporter.

It's completely irrational but there it is. And I suspect a lot of people feel the same way too for some reason.

I guess on Patreon you are buying a bigger number on the creator's page. The other reason is that it gives you a consistent "workflow" so it is easy to subscribe and unsubscribe. Meanwhile if you wanted to help a youtuber who was sometimes streaming on twitch your only option would be to subscribe on twitch even though you mostly watch the youtube videos.