The reality is that OnlyFans wasn't the first to try this model. You have to give them credit for successfully building the business, especially with several close calls between them and government regulations.
The problem is the payment processor. How the heck do you accept adult-content related payments? That is the hardest problem to solve when it comes to these things in my book.
It's beyond knowing the business model, I guess the founder were at the right place and right time and knew the right people to make this venture succeed.
Also, the marketing, how the heck did these guy blow up so fast. The funds for marketing and all, it's not cheap!
Really though, the primary reason why a company like stripe don’t want to be involved with these types of business, is the very high levels of fraud and chargebacks that come with the territory. Turns out people get embarrassed about porn appearing on their bank statements, and often put in dubious chargeback claims. Not to mention many banks have their fraud controls set to a hair-trigger for anything porn related.
The end result is processing these transactions is normally very expensive and high risk, due to the fraud and chargebacks. Which in turn put you at high risk of being kicked of the Mastercard/Visa networks. Mastercard/Visa mostly don’t give a shit what you’re selling, as long as you pay your dues. But they do get very upset when it looks like your business might threaten the perceived safety of credit/debit cards. As usual, protecting profits is treated much more seriously, than preventing any perceived moral failing.
As for governments, they officially don’t care. Selling porn is perfectly legal in the western world, so it only individuals in government who choose to abuse their positions to enforce their personal moral code on others (beyond what the law requires) that creates any kind of government “policy”.