The Belgium international completed a £28m transfer to Goodison Park on Wednesday, the place he spent last season on loan, but not before Mourinho offered his take on the situation.
"The thinking behind the move was the fact that Romelu was always very clear with us, in his mentality, in his approach, he was not highly motivated to come to a competitive situation at Chelsea," said Mourinho.
"He wanted to play for Chelsea but he wanted to be clearly the first choice striker, which in a club of our dimension, it is very difficult to promise to a player.
"That reduced immediately his desire to come to us. Everton came in with an important offer. It is the reality of our club that we want to do things really well and to always be inside the rules (of the Financial Fair Play regulations).
"Financial Fair Play is always behind the thoughts of the Chelsea board and when you have the chance to create a positive impact in Financial Fair Play, Chelsea always analyse these situations."
Mourinho was also keen to emphasise he has nothing against Lukaku and wished him well on his permanent move to Goodison Park for a club-record fee for Roberto Martinez's side.
"The important thing is he is happy and things work out for him. He is a good kid," added Mourinho.
"The only thing we can do is wish him well."