There was a point in time where NY couldn't pay a team to take J.R. in a trade. 2 years later, and he's an NBA champion, damn near model citizen and an integral piece of a team trying to repeat.
Certain guys need the right situation to grow up and refocus. Maybe Cleveland will be that for Sanders. If it isn't, he'll be gone fairly quickly and at relatively no cost to the team.
Ultimately, a guy like Sanders needs a team like the Cavs to believe in him to get another shot. A contender, with a good infrastructure and team culture, that allows him to be in a perfect situation. Without that, it makes little sense to gamble on him. The nature of him not having options is a result of many teams thinking it is not worth the time (because they don't have LeBron, or a title, or a good culture, or all of the above).
The Cavs think it is a calculated gamble worth taking based on culture, cost and Sanders remaining talent. It's a decision many other teams can't consider making because they don't have the ability to insulate him from the noise.