I'd say it's not the parties specifically, but the incentive structure created by how Congress is organized that does it. Every congressperson has their own projects they want to get off the ground, and one of the best strategies for an individual to get their bill passed is to rider it onto a different bill that might get passed. Incidentally, this is also the source of a lot of "X senator voted for Y Bad Thing" because the main body of the bill was probably about something else and they ended up voting for the bad thing too.

It's a form of the prisoners' dilemma, where looking out for your individual self interest results in a far worse outcome for everyone, and it's one of the reasons why proletarian democracies tend toward single party dominance instead of multi-party chaos (even though this makes it easy for bougie media to paint them as "undemocratic").