It's all about control of reach.
If I was an influencer and using Patreon (I'm neither), it's a simple decision:
Total reach * conversion rate * platform commission = income
Apple's app store has a fuckton of desirable reach - they monopolize (arguably literally) all the easy payments from iphones and kill anybody else who tries to redirect eyeballs. They are too strong. But what else are you going to do if you need Patreons or app customers, etc?
You can't ignore the reach, and you'd have to pay or work harder to get eyeballs another way too unless you can get free publicity by being crazy or something and pull people into your own payment/ download channels.