Lukaku signed for Everton in a club record £28 million deal yesterday.
He said: "The thinking was first of all the fact that Romelu was always very clear with us that in his mentality and his approach he was not highly motivated to come to a competitive situation at Chelsea.
"He wanted to play for Chelsea but clearly as the first choice striker which in club of our dimension very difficult to promise to a player that status. That reduced, immediately, his desire to come to us.
"After that Everton came with an important offer and as I always say, because it's the reality of our club and we want to do things well and be inside the FFP rules, it's always in the thoughts of the board, when you have the chance to make some movement that create positive impact on FFP we always analyse these situations."
Mourinho wanted to emphasise there were no hard feelings in the sale of Lukaku: "The important thing is that he's happy and things work well for him, he's a good kid and has his way of thinking and organising his career project.
"All I can do is wish him well. He deserves luck and to be happy."
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