To be fair, Trump's FCC was pushing STIR/SHAKEN hard but it takes years for the major telcos to implement and push it downstream to all of the various SIP providers that buy numbers from them.

https://en.wikipedia.org/wiki/STIR/SHAKEN#Implementation

Biden's FCC is able to take action because those were finally finished and now can enforce with the call source traceability they didn't have a few years ago.