I am a US citizen living overseas. I have a US cell number that is only used for 2FA for US financial institutions. No one else has that number. I get more scam calls every day on that number than I do in a year on my local number. It's crazy.
Most of the world has solved the worst of the problem by simply not allowing caller-ID spoofing and by blocking bad actors the way that ISPs block email coming from known bad IPs.
The US already has the STIR/SHAKEN authentication protocols, but the telcos seem to feel no financial or regulatory pressure to clamp down on all the sketchy intermediate carriers the scammers use to bypass them.
Maybe it's America's love of "market-based solutions" that prevents of from solving this problem the way everyone else has?
Rather then actually solve the problem via regulation, the US prefers to turn it into business opportunities to make the situation suck slightly less by letting the telcos sell subscriptions to moderately effective blocking programs and an creating an ecosystem of moderately effective apps.