If the government cares enough there's still a way to deal with that. Telcos could be forced not forward spam calls and allowed to not accept connections from known spam sources. Then the foreign telcos would have to choose between cleaning up their act or not being able to route calls to the US anymore. Technically that's easy to implement on peering level.

But international routing is still relatively expensive. In most cases your "international" incoming call is just a local one with spoofed source.

or someone whose story is "idk someone on craigslist paid me $300 to set up a business phone account". They'd want these anyways to ensure that they retain access in case of the network actually shutting them out.

...or consent. Seems like Marriott should get a say in the tracing of calls from people claiming to represent Marriott.

They (or whoever is transiting their lines) know the account number of the entity that pays for the line that the robocalls are originating from. If the phone company made it possible for end users to block numbers based on who is funding the calls I think they would go away fairly completely.