They don't. It's just that the solution to scam voice calls is a lot harder to implement--there's no point making rules to address voice calls because there is

They don't. It's just that the solution to scam voice calls is a lot harder to implement--there's no point making rules to address voice calls because there is not yet the technical capability to follow any rules around that. The STIR/SHAKEN protocols which will address voice scam calls when they're fully deployed, but that's a fundamental change to the protocol, which takes time. Texts, on the other hand, can be text scanned independent of the number from which they originate, which allows for a lot of filtering.