I think a lot of people think the processors are doing this out of some moral high ground to try and kill off the pornography business, but that's not what's happening. It's all about risk and opportunity cost. I forget the exact numbers, but pornography and gambling are near the top of the list when you look at industries with the highest number of fraudulent transactions. When someone reports a transaction as fraudulent, the money to refund the customer comes out someone behind the scenes pocket and often that money gets tied up in limbo while everyone points fingers at everyone else. Dealing with fraudulent transactions is a massive headache that wastes a ton of time.
Most major processors just don't want to deal with the hassle and the ones who do charge extremely high fees to offset the extra risk. OF has probably been using a processor that doesn't allow for pornography this whole time, but the processor has been letting it slide. My guess would be the risk has finally grown too large and the processor is cracking down. Like I said, there are other processors out there who are happy to work with the porn industry for a much higher fee, but it seems like OF has decided for one reason or another that that isn't as lucrative as just banning explicit content all together.