They're not obligated to, just as I'm not obligated to accept a check from your bank and can demand cash or some other form of payment. Your question is like as

They're not obligated to, just as I'm not obligated to accept a check from your bank and can demand cash or some other form of payment. Your question is like asking what if no one wants to talk to me with PGP or some other secure message protocol. What if selling things to US citizens via any means is criminal, and enforced?