In fairness Lukaku is still a bit of a raw talent, we can see that ourselves when he plays, he is not the finished article by any stretch. His touch and decision making at times can let him down. At Everton he is forgiven that as he's still learning his trade, and lets face it we've been crying out for a decent striker for a long time, but Mourinho seems to prefer more experienced players as he likes them to play a disciplined tactical role. Eto'o may just need time to settle, or maybe he over-estimated his physical condition. I remember Eto'o as a kid at Real Madrid, he's been around forever.
He spent time with Lukaku before loaning him out, he maybe felt he wasn't quite ready for their first team, but it would hinder his development if he didn't play regular football.
I think Drogba is a great shout and strangely would like to see him back in the Premiership.