According to Brian Windhorst of ESPN, LeBron James has signed a two year deal with the Cleveland Cavaliers, and has the option of opting out next summer and being a free agent once again. James, however, is said to be completely invested in the Cavs long term.
Because players are eligible to earn up to a certain percentage of the salary cap, James is simply keeping his options open to make as much money as he possibly can. If he locks himself into 25% of the cap while it is projected a little over $63 million, he will make less than if he's making 25% of a salary cap closer to $80 million. That type of jump could very well happen, and it makes sense for James to capitalize.
By doing this, James does open himself up to risk. NBA contracts are guaranteed, so if James requested that the Cavs complete a sign and trade, James could have been eligible for five years and around $120 million. LeBron James has never been seriously hurt, and can take the kind of risk most players can't. He could miss all of next season, become a free agent, and have every team in the league willing to offer him the max.
While it would be nice for the Cavs to lock James into a set amount, it appears that James wants to end his career in Cleveland, and it's well within his rights to earn as much as he can. In the meantime, Cavs fans can celebrate that LeBron's return is now official.