Caller ID is a bit of an afterthought hack added to the system so it's not really built into the original design of phone systems. There's not really the valida

Caller ID is a bit of an afterthought hack added to the system so it's not really built into the original design of phone systems. There's not really the validation built in for a phone company to validate that the phone number sent from another network matches what they get is the target number and some caller id info to continue connecting the call. Add on top of that the fact that phone companies are required to connect incoming and transit phone calls and you get the current mess. Phone companies can't refuse to connect calls systematically from a bad actor and there's no validation mechanism because only the caller's phone company actually knows the initial number for sure.