I know what everybody's thinking: visa/mastercard is playing world morality police. But most of the major payment processors have banned certain types of products from being used on their platform[1], some of which obstinately lacks a "moral" reasoning (see: virtual game currency). My guess is that those types of businesses attract a high fraud/chargeback rate, which makes them more expensive to process. It's a risk/benefit trade off, nothing more.
In fact, high risk is just another way in which VISA and MC will squeeze merchants, it doesn't matter to VISA because they pass all of the risk to the merchant anyway.
[1] https://stripe.com/gb/prohibited-businesses
https://www.paypal.com/gb/webapps/mpp/ua/acceptableuse-full
https://docs.adyen.com/legal/adyen-restricted-prohibited-lis...