Genuine question from someone who thinks they understand the tech: I don't get why I haven't seen a whole lot of (or any) of these models or tools "self report

Genuine question from someone who thinks they understand the tech: I don't get why I haven't seen a whole lot of (or any) of these models or tools "self reporting" on "confidence in their answer?" This feels like it would be REALLY easy; these things predict likelihoods of tokens -- just, you know, give us that number?