Because not everything is distributed on YouTube. I support writers and artists on patreon. That's the bulk of what I support. Even if we say Google, youtube creators already complain about youtube and how it squeezes them so is it really better? Youtube even has a patreon like thing, but creators prefer to diversify the platforms they are on. Especially if, as is common, what they are selling on patreon are things that aren't allowed on youtube.