I would also like to add Ease of Use to your list.
I have had to help several of my Patrons with basic tech support issues, like setting up RSS feeds in their podcast app. And I doubt that they would be able/comfortable with working with a service that is not as easy and straight forward as Patreon.
- Payment processing: Patreon consolidates all payments under one gateway account so fees are low for everyone.
- Support: What happens if the payment fails? Creators don't want to deal with that mess every month, it's less time to do useful stuff.
- Abuse handling: Patreon can deal with spam comments and the like.
- Service hosting: They integrate all this stuff in one place that creators don't have to host themselves.
- Consolidated management for Patrons: As a subscriber it's nice to see all the stuff I'm supporting and how much I'm paying for it in one place.