If you could enforce that the outbound caller ID matched a valid inbound number, that would solve a lot of problems. (1) if a number is used for spam a lot it’s gonna get blocked; rotating through a bunch of numbers per area code does get somewhat more expensive over time (and they could probably enforce a fee for connecting/transferring a number). (2) it solves the problem where regular people get accused of spamming because they were spoofed, (3) it solves the problem of fake law enforcement or government agencies “calling” you from legit LE phone numbers.

Sure, spammers could still get tons of numbers, but straight up spoofing would vanish, and that’s a big enough win.