It's not because he's anti-Semitic.
It's not because he flipped on the Iraq War and opposed The Surge.
It's not because of an anti-gay slur.
It's not because he made such a hash of his confirmation hearing.
It's because he'll dutifully dismantle the American military for his boss, thus enabling Democrats to claim that the weakened state of the US fighting machine is the fault of Republicans.
In short, it's because Hagel's a dupe.
Make the president nominate a Democrat to dismantle the military. Republicans shouldn't let Republicans drive drunk, especially when they're puking in the car.