Give Obama credit. With his bad negotiation skills, it was better for him to appoint a negotiator (Biden) than do it himself. The Dems give a little on income levels for tax increases and they let the 2% cut in the payroll tax expire. Otherwise, they get what they want. Entitlements are untouched, tax credits get extended, and Medicare doctors don't get a 27% cut in pay. The Republicans get what they can, which isn't much. The debt ceiling can is kicked down the road. We'll see if Boehner can whip enough Republicans to save face. Both sides should take the deal.
UPDATE 1: The Senate passes the deal 89-8. I don't see how the House could not pass it. Around 50 hardliners in the GOP will vote "no" no matter what. After that, there should be a clear majority vote.
UPDATE 2: With only 36% of the GOP caucus voting "aye", the House passes the Senate version unamended. The final vote was 257-167.
UPDATE 3: The short answer to the article title is: Because he's a douchebag. The long answer as to why Reid ended negotiations and Biden stepped in is here.