It actually startet a couple of years ago, with an us-bill from 2018 called FOSTA/SESTA.
Its intent was to stop sex trafficing but because of its phrasing/wording it kinda targeted everything sexual that's in some way illegal
(no matter if real or cgi/drawn) and made it that credit card companies are accomplices when used as payment methods for those kind of things and can be held fully accountable to punishment.
Fearing that they will end up in court, the credit card companies threatened all sorts of porn and NSFW sites to withdraw their services if they did not remove such content and change their policies.
Of course, most complied, even such a big site as PornHub. Others have perished because of it.
That's also the reason so many sites have changed their NSFW policies within the last 6 years.
So it's not that the credit card companies want to do that, after all they are missing big money because of it.
One must not forget that companies are not people, they have no morals, they only care about money and their public image, which in itself affects their revenues. Every decision they make is money oriented.
TL;DR: New Us laws in 2018 -> credit card companies might get punished -> they force websites/-services to change their NSFW-policies -> no lewds for everybody anymore ->