Here's my reasoning... he's from Cleveland, his wife just posted "home sweet home #330" on instagram regarding Akron. They stay there every off season. He hated the way the decision played out for him. He's got his two titles now and still he deals with constant bs from detractors. I think he's content with two titles and would rather shoot for the moon and go back to Cleveland. Best case he brings a title to Cleveland and is the savior afterall... worst case they never win it, but at least he's once again beloved in his hometown.
He's not motivated by forming another "dream team" wherever the pieces fit I don't think. Been there, done that. Two championships but I don't think he really enjoyed his time in Miami... not like if he would if he goes home and has success. Time to think about after basketball stuff for Lebron... he's going home.