Slate: Why It's Going to take so long..

According to John Dickerson, because this is how the sausage is made:

Much of the time between now and when Obama signs the bill will be spent acting out the new era of politics he has promised. Much of Obama's popularity is based on his promises to build bridges with Republicans and change the way Washington works. Obama "really does want this to be bipartisan," said one veteran Democratic Senate aide when I asked why Senate Democrats couldn't just push through the Obama program quickly with their new massive majority. According to one participant in Obama's Monday meetings with Republican leaders, he stressed that he wanted "substantial Republican votes" in support of the bill. He promised that while he wouldn't agree with every idea, he would listen.

Republicans will have to get comfortable with the stimulus bill's contents and find plausible explanations to offer their constituents for their yes vote. (In meetings with Obama, congressional Republican leaders said his proposal for $300 billion in tax cuts will help them make the case.) Unlike recent unpopular recent bailouts, this one is targeted toward regular people, which should make it easier for Republicans to explain. But GOP legislators don't want to look like they're just writing a blank check to a government that President Bush has already put into historic bloat. (Some Republican strategists argue that a symbolic fight over spending would be a useful way for Republicans to show that the party had broken with the Bush era.)

The process of winning over members in the minority party—or at least making it look like they were given a fair role in the process—will require patient negotiations and perhaps committee hearings during which Republicans are given sufficient time to ask questions and perhaps even call witnesses. If Obama wants to embrace their contributions to the bill—one of the biggest signs he's making good on his bridge-building promises—he'll then have to make sure he shows the same concern for the views of his fellow Democrats, like the deficit-conscious Blue Dog Democrats who want rules written into the bill that link future spending to corresponding budget cuts.

One way Obama could grease the legislation would be to allow members to fund pet projects through earmarks. But he's said he doesn't want to do that. Obama has promised the bill will include no earmarks. That's an honorable position, but it creates a second problem. He's raised the bar on the kinds of programs that will be funded by the legislation. Some of the infrastructure programs governors and mayors have suggested are "shovel ready"—meaning they have all the permits they need and are best prepared to take advantage of immediate federal dollars—aren't technically earmarks but can sound like pork. "Part of the charge of … our budget team is to make sure that we are proceeding on projects and investments based on national priorities and not based on politics," he said last year describing his "new way of doing business." Figuring out how to move quickly while retaining some level of federal oversight will be complicated.