In my experience, having worked at several large PSPs, it is Mastercard and Visa who are the morality police. Stripe are just enforcing the rules insisted on by them, and PayPal forgot about them 3 layoffs ago.

Then how do other processors go over the Visa and MC rails for these transaction types? How does Stripe allow some and then block others?

Simply put, Stripe doesn't want to deal with the risk associated with those transaction types.

I know it's about risk. Perhaps my point was not clear?

Simply put: Stripe selectively applies their own policy about "restricted" transaction types.