I would disagree with this. I think it is to do with ability. Roberts doesn’t actually do anything. Doesn’t score, assist, create chances or normally even retain possession.
He’s “exciting” because he tries dribbles but in both of his spells has given us very little.
Then add in the defensive side of the game and I can see why he’s not in the team.
What I really don’t understand is why he was brought back.
It's really weird. First thoughts are he's just not a hard worker and doesn't have the defensive skills Warnock requires. But then he managed him for a couple of months last season so he wouldn't bring him back if that's the case.