Detroit didn't lose him for nothing, they got a productive player on the cheap for 4 years and will get him for a discount next year. If they let him walk then they believe they can get better players for the max, and in almost all cases it's better to let an overpaid player walk then keep him around when you can use that cap space on someone better.
Detroit Pistons' Greg Monroe urinated self during arrest, police report says http://www.mlive.com/news/detroit/index.ssf/2014/09/detroit_pistons_greg_monroe_ur.html