Because he’s horrible; it’s the only explanation.
I think we all need to understand just how bad a 1st round pick has to be for their team to bench them, especially for the types of players he’s being benched for.
The coaching staff wants badly to have this player on the field, trust me. But they have a lot more data on him than we do, including assignment execution and practice reps, and if they’re saying they can’t play him, the only conclusion we can draw is that the guy is just flat-out awful, worse than any of us realize.