In Patreon’s case, rather than specifically wanting to crack down on porn (which would be rather strange, as Patreon has a long history of having its most successful creators be porn artists and developers of porn games, much like how gaming content accounts for a significant portion of monetized YouTube videos), it’s probably because they accept PayPal, which doesn’t allow you to use it to pay for porn, combined with a general crackdown on content of questionable-at-best legality (like depictions of underage characters).