Isn't this what free apps like HiYa and TrueCaller do?
With apps like that, you're still getting the robocalls, you just don't see them. The carrier still has to carry them. They take up bandwidth on the trunks and frequency allocation on the cell towers. The ones that originate as VOIP sessions from some boiler room in Bangalore clog up valuable spectrum on transatlantic cables. The earlier in the process they can be blocked, the better.
Those are all still problems, you are right.
But, they are now the CARRIERS's problem, not mine.
It's their problem to fix anyway, so that's right where the pain should be to get the issues resolved.