Because Dems are looking at the shiny coin: voter suppression
Howard Dean took this on in 2008. The fact that no other Dems jumped on board or that the media didn't pick it up is beside the point.
You kind of typify what (I believe) is wrong with our party. You've used a RW talking point against yourself: "The Dems will cry foul if we (Rs) win." So what do you do? Like a good Dem, you're afraid to cry foul because the Republicans will say, "I told you so!"
Dems let Rs paint themselves into a lose-lose corner.