Arnorld Kling thinks he knows what’s up:

I think the answer is that it is a reparations bill, not a stimulus bill. People who pay income taxes tend to vote Republican. People who live off taxes tend to vote Democratic. To the Democrats, the Bush tax cuts were a heinous evil, comparable to Germany’s violation of Belgian neutrality in World War I. Now, they are demanding reparations, with hundreds of billions of dollars to be paid into teachers unions and other members of the coalition that won the election.