Because conservatives won't go for it:
Mr. Obama, seated between Mr. Boehner and the Senate majority leader, Harry Reid of Nevada, told the lawmakers he would not sign an interim deal, only one that extended through the 2012 election.
Then he surveyed the eight leaders about their preference for three deals of different sizes — the largest being up to $4 trillion in deficit reduction over the next decade, according to aides briefed on the discussion.
Six of the eight expressed their support for the biggest deal, the aides said. But Representative Eric Cantor, the House majority leader, and Senator Jon Kyl of Arizona, the ranking Republican on the Senate Finance Committee, favored the midrange $2 trillion, voicing doubts about how they could sell a $4 trillion deal to their rank and file, officials said, since it would involve tax increases.
It's interesting that John Boehner is apparently open to a grand bargain. Maybe, lurking beneath that tanned face and hackish career is the soul of a patriot, or a deficit hawk, or prospective future member of blue ribbon panels. Possibly Boehner's hours of discussions have persuaded him that he must abandon party orthodoxy to address the deficit.
It still doesn't matter. If Eric Cantor doesn't want to pass a budget deal, then the chances of it making it through the House are zero. If Boehner and Cantor and Paul Ryan pushed for a deal, there'd be a chance. But even the medium-sized deal will be hard.