I imagine it has changed, but 10-ish years ago I recall having a cheap VoIP account that just let me enter whatever phone number I wanted as the caller ID.
It's very much a "honor system". If VoIP provider doesn't do due diligence, the other networks can't really check the value, especially since number porting became norm
For the first few dozen times sure, but after the hundredth or so report of a scam call associated with a spoofed number, the VoIP provider should be blocked by the telco. That is if they were allowed to do so.
