None of the 4 players you mentioned are academy lads. What is our attachment to Unal? We bought him from Turkey and loaned him out, the only attachment people have is that he is a young prospect, not that he is grew up playing in Manchester.
Also, how have we treated any of these players poorly?
Mooy: Plucked from crappy Australian league to now being a premier league player with Huddersfield, I bet he's super pissed about that.
Moreno: From Columbian league to ply his trade in the Spanish league, logical choice because the environment and language shouldn't be too difficult for him. Up to him to prove his worth, which he hasn't.
Unal: Taken from Turkish league to play 2nd division dutch football -> 1st division dutch football -> 1st division spanish football, hence he is constantly playing in a more difficult league and improving (how could a player be mad about that?). He is playing for the 5th best team in La Liga now.
Roberts: Taken from Fulham and put into our academy for a season, judged to be a top prospect, so placed in Celtic who are the best team and play attacking football, even moreso under Brendon Rodgers who has developed him better. What happens next is down to City management, should either be brought it or loaned to the 1st division in Spain or Germany.