He was originally nominated for SCOTUS by Obama to be that centrist pick.
But he was hired by Biden as AG after having that opportunity permanent denied him, embarrassingly and publicly, with the thought being that he’d be ready to pursue the types of people that used his legacy as a pawn with vigor. When he was nominated, general thought back then was that he may be ready to pursue his work with more intention as a result of what had transgressed.
If not for the Obama nomination and SCOTUS denial I would agree with you, but there was supposed to be more to him after having endured the gop’s horseshit, when in any other time in our history he would have just been a rubber stamp approval. Garland probably would have been a good Supreme Court Justice for the same reasons he’s a horrible failure as AG.