I think this all comes down to how incredibly divided the two parties are. It has gotten to such extremes that you are one or the other and you are vehemently against anything the other side stands for.
Because of this, both sides are willing to push the narrative that the federal government is full of career politicians who don't care about the people and are only out to evilly push through whatever their party wants. Think of it as political cronyism. A bunch of bloodsuckers who only want to keep themselves in power.
Call me naive, but I think that that a lot of people still enter the political realm with a desire to do good and actually solve existing problems.