why would a bad team like the wiz just give away a guy averaging 13 ppg?
Because he causes more damage to his team than he helps them.
He is like a miniature version of Monta Ellis. Unable to play the PG position because he cannot run a team and unable to play his natural position at SG because he cannot defend opposing SGs.
Too inefficient offensively. Too vulnerable defensively. Streaky player who more often hurts his team than he helps them.
I've never been huge on +/- stats, since they depend on who you see playing time with, game situations, etc..., but I'm a little alarmed that the Wizards are substantially worse with Jordan Crawford on the floor, 3 years in a row. The Wizards have been a pretty bad team the last 3 years.
Your +/- may suffer when you're backing up John Wall on what's otherwise a horrible team.
It may, but that doesn't really seem to be the problem with Crawford.
Wall has missed about a third of the Wizards games so far in 2012-2013, so it isn't only units with John Wall that are outperforming units with Crawford. Units with AJ Price at point guard and units with Bradley Beal at point guard have outperformed units with Jordan Crawford.
And in 2011-2012 and 2010-2011, Jordan Crawford played most of his minutes with John Wall on the floor, via 82games.com.
The team has been worse with him on the floor for 3 years running, even when he is playing with Wall and even when compared to point guards that aren't Wall.
This is particularly alarming, because as you have noted, the Wizards are a horrible team. AJ Price isn't setting the bar very high.