In order to stop robocalls, you just need to do three things:
* Flat out ban them and make it illegal to route them at network handover points
* Make caller ID mandatory with a reachable number to call back to
* Create an authority caring for those robocall reports
Then, put heavy fines on violations and go enforce the heck out of it. That's exactly what the EU did pretty much in the infancy of this technology.
I can't recall ever getting a robocall here in Germany.
That being said, my bet is this being a tragedy of the commons, as the only two parties in the system seem to heavily rely on the tool for fundraising — oh and they probably also make millions for some selected members of congress... ¯\_(ツ)_/¯