It's not a good trade for Detroit because most of the possible outcomes of the trade are bad. First off, he's not going to make a significant difference in their win total this year. Second, he will either leave or Detroit will overpay him to stay. The first outcome is bad, but the second outcome isn't great either because they'd be paying a lot for a guy who isn't a star.
The best outcome could be the Pistons dealing him to a contender in 6 months, actually. I wouldn't be surprised if that's what happens.