Would you launch your new line of e-books on a site that is 95% porn and well known for porn?
No.
If you're a porn site, then you're pretty much going to be just that, it's its own content vertical, fairly distinguished from everything else.
Amazon is not known for porn. I didn't even know you could get porn there. Certainly, it's not 'online porn' which I would imagine would be the primary issue.
Tumblr became a place known for adult content so it was a problem. If Amazon started to do a lot of digital porn, like PornHub, it would be a problem.
If there is no 'search' on Patreon ... maybe they could keep it hidden. But it's a big risk.