In Patreon's case, I don't think the user found the content "through Apple". The customer found the creator, and the creator said "Pay me through Patreon". The user, only having an iOS based device is now trapped by Apple's restrictions on the transaction, which brings dubious benifits to the table.
That horse has left the barn. But if there was a conceivable way and leverage to get a cut on paid content on the open internet, I'm sure apple would find a way to coerce money from those visits too.
One analogy: By offering only Fairplay DRM on iPhone, they get a cut that might otherwise have gone to Google (widevine), Microsoft (playready) or some other third party.
