As alluded to by morkalork, they definitely could if they wanted to, as the (most? of the) rest of the world doesn't seem to have this problem. As long as spammers keep paying telecoms & no law(s) forbidding this exist, it will continue.

edit: grammar

> As long as spammers keep paying telecoms & no law(s) forbidding this exist, it will continue.

That's the trick. A lot of countries bill calls to cell phones at 10 cents a minute; in the US, calling is near zero cost. The US makes a great market for scammers to target because of low operating costs, penetration of globally usable payment cards, minimal language diversity.

Of course, these scams are forbidden by law, but that doesn't change the economics. Very few scam shops get busted; especially when most of them run from outside the US. STIR/SHAKEN helps a bit, but not much... without a effective mechanism to report unwanted calls that leads to those callers being ejected from the network as well as ejecting providers that are unresponsive to reports, there's not really hope of progress.