This all started way, way before Pornhub.
First it was federal and state moral laws (mostly porn, but also race and gender related stuff) with state/local and USPS cops handling enforcement, back when there was no internet and the way you got information out was via newsletters, zines, and such. USPS cops used to literally spend their days steaming open envelopes and rifling through people's packages that seemed like they might contain lots of flyers for unions or newsletters for black panthers, or nudie mags. But religious conservatives lost court cases left and right, eventually giving up on that front.
So they shifted to banking to enforce a moral code in the private sector they couldn't do so via the government. After all - if you can't ban something, just starve it of money...making it impossible, or very expensive and inconvenient, to fund.
For decades, porn stars have been basically shut out of the banking system, blacklisted, finding their bank accounts suddenly closed with little warning, with little or no explanation. I'm not talking prostitutes - I'm talking people who are clearly employed and receiving paychecks for being adult actors in films, all very verifiable. What's wild is that clearly banks are spending labor and resources to have computers and staff go through and find these accounts and close them.
Criminals figured out pretty quick that porn stars had lots of cash hanging around, and they became targets for both organized (and less so) crime...as well as a place for organized crime to dump/launder money.
The credit card industry claims they restrict / charge such high fees for porn because of fraud rates, but...look at the gym industry, which is infamous for fraudulent billing practices, and how they have access to credit card processing and even ACH access. The banking industry also seems more than delighted to handle the finances of boy scout troops and catholic churches.
When ads dominated revenue, that was how censoring happened - major advertisers would contractually ban adult content from sites running their ads. With subscription fees taking over, it's now credit card payment processing. Most of the major crackdowns on adult content on various platforms have come from merchant and processing banks threatening to pull service because they don't like what they see on the site...or from the site trying to get an app onto Google and Apple app stores.
Speaking of which: that's also why Apple is so paranoid about adult content in apps, podcasts, etc. They make a massive amount of cash off their take from app purchases and subscriptions. Even a slight increase in the percentage they pay, due to "risk" or some percentage of the fees going to adult content - means a huge, huge loss in revenue for them. Well, that and I think Tim Cook has internalized a lot of the conservative "gay = child predator" stuff which is why he's so fucking obsessed with Protecting The Children (coughCSAMcough) - but that's another story.
ChatGPT, by the way? They didn't implement prudish (and pretty ineffective) censoring out of some moral code (otherwise they would have better filtered the training set, which clearly contains a LOT of porn), they did it to satisfy their credit card processor. The really big crackdown on naughtiness recently? Notice it happened right when they were submitting their iOS app for approval...