Or, to look at it another way... All the other payment processors have settled on needing to earn and average $0.50 / transaction in order to make a profit. Then they calculated their average transaction and came up with a 3% (or 2 or 4) being required to make that amount.

Then Patreon came up with the same $0.50 / transaction number. However, since their average transaction amount is so much lower, they have to charge a higher number in order to make their target.