Any bill that is that important and that uncontroversial has got a lot of political potential energy. And that means that politicians can take some of that lack

Any bill that is that important and that uncontroversial has got a lot of political potential energy. And that means that politicians can take some of that lack-of-opposition, add some pork, and wind up with a personal benefit and a slightly-less-unopposed bill. The end-point of this process is that most bills will barely pass, unless they're so hot politically that it's easy to attack someone over messing with it (think some of the post-9/11 terrorism related votes).