This matches my experience.
The US seems to have completely given up on protecting its public phone network against abuse, while at the same time relying on phone numbers as the primary identifying key and authentication method for humans in countless business processes.
It took years (if not decades) of regulatory neglect to get that bad; I doubt there’s an easy fix at this point. It’s really concerning.
It's not a prefect system but I don't use a landline and set unknown incoming numbers to silent unless I'm actually expecting a call. Someone important trying to call can always leave a message but the spammers never have.
I suspect that the main reason is that politicians rely on the same mechanisms as robocallers and spammers, so they don't want to restrict it.
Sometimes, I get robocalls from local PACs, and they get automatically flagged as scams, because the dialer companies that the politicians use, are ones that also run outright scam campaigns, and get blacklisted.