The non-spammy network operators that interconnect to the spammy network operators make money through that interconnection. If you want them to disconnect their spammy customers, you have to convince them that it's worth it to lose them. This is a manual process and takes time.

This is where infrastructure level legislation comes in. They should be required to provide the full originator information all the way to the people who receive the call, they should block known spammers, they should block other networks that do not do this, and they should be fined heavily if they do not. Otherwise the phone system will become a relic.