Because he knew he had little chance of getting reelected otherwise, so a failure would cost him little.
If Obama and his handlers think that this is going to float him through to re-election, they've got another think coming. Over the next 18 months, the American people are going to suffer through one of the worst economic downturns in living memory, which is a guaranteed deal-breaker for re-election.
And, all of the things that gave birth to the Tea Parties aren't going to disappear before election day, and Obama isn't going to do a damn thing to correct them. He'll get a short-term bounce out of this, and nothing more.