I don't get this, and I'm not defending him, but he's only been at a few prem clubs, he hardly got any game time at Chelsea, but he always said he wanted to stay and fight for his place, went on loan to West Brom, got his head down, and did the bizz there, loaned to us, got his head down, and did the bizz, signed for us permanently, did the bizz, and then had a proper whinge the last few months of his time with us, so in reality the only time he's had a proper moan at a club was towards the end of his time with us.
Also, there can be a case for him being cheesed off at Man U (if he actually is) at this moment in time. I said it before on here, but my missus's dad and brother are Man U fans, and they've both said that the way Mourinho has them set - up doesn't suit Lukaku because he's always having too drop deep looking for the ball, and when he is making runs, or is in space Man U players aren't releasing the ball quick enough, so you could understand if he's frustrated.