Two of them are players who wanted to leave, and the third (Kean) was moved on willingly by his agent. I don't see the relevance. I'm not at all interested in trying to keep players who don't want to play here.
Raiola wanted Kean to be a starter instead of the rotational player his level really was, so he went to Everton, flopped (not exactly a surprise for a 19 year old Italian), and now he's doing well in a weak league for a strong team where the front 3 or 4 players score a lot of goals every season. Icardi has already missed over 20 games this season through illness or injury so he's going to play.
I can understand and agree that it's a shame how we rarely develop players for the first team, get a good one, and then 5 minutes later he is gone, but that's just modern football. Since the millennium agents came into the fray and they make the moves happen, there was never going to be any settling-in period for him, earning his dues like there used to be for young players. Everything has to be now, and that goes for players, agents and fans alike.
Also, we're not a club noted for developing players. Raiola's comments about us playing him in the U23 are obviously absolute rubbish, gross exaggeration by him, but you can look at our record with young players and use it as an argument. It also depends on the individual as well. Kean has his own mind and he seems like a typical modern player, but others who come through like him might not be of the same mind as him, and won't have Raiola as an agent.
A personal view - I don't think Kean is a top striker or is ever going to be one, but I'll be glad to be wrong as Italy are crying out for one. He's a striker who fights for minutes at a team like Juve with someone like Morata. But that wasn't enough so he moved on, life goes on.