skoadam, you kinda answered your own question. The Heat are going young with Josh and Winslow. They didn't want to pay Wade the money he deserves/wants.
In all contract Wade signed with the Heat, he willingly got shortchanged in each every one of them, all in the name of the team. After LBJ left, he finally thought 'time to cash in' but the Heat had other plans. It led to this.