[hinkley]

In theory aggregation and distribution allow for lower transaction overheads but in practice the middleman seems to keep a lot of the money.

Fifty people donate $20 each, to be divided between 100 recipients, that's 150 transactions (50x$20, 100x$10). As long an the donations are earmarked for more than 3 recipients per donor, that works out as fewer transfers.

Apple Music in theory could have paid artists more, but I haven't heard any news on that front since ages ago, when Weird Al puzzled out loud about how he was making about 1/10th of what he used to make.

And I thought Brave's original model was something along this line and they seem to have abandoned it, which is probably worth digging into.

I think you have to consider as well that if and when someone actually figures out how to make this distribution model work, Visa will notice and introduce their own system. They can split the difference on overhead and increase their margins while also increasing donation efficiency. But perhaps only once someone else has proven the idea (free R&D).