Depends how you view it mate, the bigger the club - then basically the smaller the window you have to impress, which is just the way it is.
He returned from the West Brom loan, and during the pre season etc didn't convince he was ready to play for them, so loaned out to a better team, repeated his scoring rate and started pretty much every week for a team that finished 5th - in large part due to him.
Returned to Chelsea - and yet again during the pre season he failed to convince the coaches he was ready, during that time i think chelsea bought Eto'o in and brought back a washed up Drogba rather than play Lukaku.
Mitigating circumstances ofc, but he did fail at Chelsea and given his frequent comments about wanting to be the clear number 1 at any team he went to then it shows that fighting for his place isn't something he relishes.
You go 5-7 games without scoring at a team like Chelsea, Bayern, Barca etc then you better be contributing hugely in your general all round play or your gonna be dropped fast, Lukaku is a pure out and out goalscorer first and foremost, at us - when he has had poor runs of games without scoring then we just keep playing him through it as we have absolutely no option but to do so, he repeats that after he moves then they will drop the player.
Only twice has he ever faced competition for his place - at Chelsea and he lost out to a ageing Eto'o and Drogba
at Belgium when he ended up being dropped for Origi during the tournament and where he has failed to get close to looking top class