Mancini generally pretty poor at giving youth a chance unless they're already established like Balo, Nasty or rodwell. Doesn't seem comfortable with the notion of players learning by doing in the city first team.
Lopes, Guidetti and Suarez (maybe even Pozo?) should be on the bench more. Guidetti simply can't be less fit than an Aguero who Mancini deems to unfit to play for god's sake. Daft to even put aguero on the bench in that case.
With the amount of EDS games he's played, he must be fit enough to be at least be on the bench occasionally. It must be that Mancini doesn't rate him.
IMO, Guidetti will leave the club this summer without ever playing a full game in the first team. Depressing.