> I'm fairly sure this is tied to anti-money laundering rules (but would be happy to be corrected). Basically, if Patreon bundled patron payments and then paid them out to creators, it could be construed as transaction laundering.

I doubt this. If I buy 10 1 euro iPhone apps in a day, Apple will charge me $10, in one transaction, then eventually pay out a euro less their fees to each developer. I don't really see why this would be different.