Because Obama has all the NSA/CIA/FBI files/dirt on all of the Republicans - blackmail. It worked on Judge Roberts vote on Obamacare, it will work again here.
You know, I can almost really believe that Hussein blackmailed Roberts, when I remember the spiteful little disclaimer in his opinion, something to the effect of “you voted for the guy, so now you can live with his actions”. It’s as if he would’ve liked to have voted according to the Constitution, but he couldn’t because of the blackmail, and bitterly threw the blame back onto the voters. He had a point, but he of all people knows that’s not how the SC is supposed to function (”you voted for this unconstitutionalty, now you get it”).