There are too many nuisance calls, there are too many people (and businesses) falling for scams, and there seems to be nothing telcos or governments are willing to do about it.
It's pretty much the same thing that's happened to Usenet and Email (and is now happening to the Web as well). John Gilmore's lament about crackdowns on open email relays is heartfelt, but ultimately naive. If I'm remembering correctly (and I'm probably not), it ran something like: We created a way for anyone anywhere in the world to talk to anyone else, and it wasn't an accident. The problem is of course, bad actors, and lowering costs means enabling vastly more bad actors.
Figuring out how to impose highly asymmetric costs --- and not necessarily financial ones --- on unwanted communication attempts, will win this.
The technical problem is reasonably straightforward. Generating widespread adoption is the real challenge, IMO.