I assume they just decided that the whole industry, even if run legitimately in some cases, has too high of a legal risk and hence don't decide on a case-by-case basis. With how often NSFW content gets reuploaded and the source becoming unclear, they probably see the biggest risk with undetected child porn on regular porn sites. If you are involved with that as a payment processor that's obviously a huge problem.

That's just crazy talk. Doujinshi isn't kitbash collages of free 4chan images. Or is that expectation of readers? If so it makes sense that those things don't come from anywhere Western.