For example, if an industry has a humongous chargeback and fraud rate, then they become unprofitable and get dropped. This is why American Express stopped allowing porn (there was news articles about it at the time and they went on record saying massive amounts of chargebacks and fraud from porn sites were solely the reasons). American Express and Visa also don't allow you to use you to use your credit card to pay your mortgage (Mastercard does). I don't know the reasons why, but I'm sure it's not arbitrary.
They also have to conform to laws and regulations. This is an offshore company, PayPal is based in the United States. I don't know if its legal to sell this sort of spamware-as-a-service in the United States, but I think there might be AT LEAST copyright issues content harvesting that they appear to be doing (based on other comments).
These are businesses, not charities.