Basically any content that is controversial for any reason, be it porn, government criticism in china or unpopular opinions, makes VISA and Mastercard wary that it will be bad PR for them, so there is some evidence that the pair is basically threaning to cut service to any of their downstream partners, for example if you google a bit there is some (sadly murky) evidence that they been threatening Patreon if they allow certain kinds of content (for example incest porn).

So people noticed many particularly sensitive political videos, can only be hosted safely on outright porn hosting sites, even self-hosting is not safe unless you also own everything else needed, because the CC providers have firepower to threaten almost any company they wish to, including ISP, DNS providers, etc...

But that's actually predictable. Banking is built on trust. Trust is a societal construct. "It's hard to open my porn shop because the banks won't give me a loan and the town won't zone for it" is an issue older than the Internet.