I think the real reason is more complicated.
Alertpay was fallen ,because one of the employees have approved cp and drug selling websites to use alertpay as a payment processor.After that alertpay got banned by visa and mastercard,and have no options to continue payment processing.This is the sad storry.
Alertpay was canadian based payment processor,where legal porn is allowed.
Now,payza operating in UK,maybe this is why they dont allow porn websites.