They did because they want you to use the credit card they are coming out with this summer. I will guarantee they will allow you to send cash to a person leveraging the new credit card.If you send cash to a friend using a credit card, that's technically a cash advance. Apple's design was following the rules. It's cash. Other companies that do this may be treating it like a service and therefore charging the card a merchant transaction, but that's bending the rules a bit. Removing the feature was the best course of action.
It is a coincidence that the day the announce their card they stop allowing Apple Cash via credit card?