In my younger and more vulnerable years, I was far more interested in politics than I am today. Although I'll make jokes on Twitter or listen the occasional podcast about current political events, I have shifted my focus elsewhere.
When my feet were firmly planted in the political sphere, I had certain opinions of course but I still had a collectivist backdrop that informed all my conclusions. I believed in the Constitution, in democracy, and yes, bipartisanship. Even though I thought small government was better, I was still working inside that paradigm.
What brought me out of this trance was Austrian economic theory. Scarcity exists so people are forced to make choices based on that fact. These decisions are always directed by self interest. Value is subjective. The conclusion of all this is that people value certain things more than other things, and they prioritize those things over others.
I used to think that politics was an arena devoid of selfishness where people argued by reason to make decisions for the common good according to the will of the people. Not only is this false, it is impossible. Politics is just like any other area of life, and in many ways it is worse in this regard because politicians have no skin in the game (shoutout to Nassim Nicholas Taleb.)
The point is that there is no Platonic form of "bipartisanship" that people love to idealize. It doesn't exist. People don't do things for the sake of them. They act according to what they value. This doesn't mean that they'll always be "selfish" in the traditional sense, and every situation is a cash grab where other people or nature or self actualization mean nothing to them.
The only exception to this would be if somebody valued bipartisanship for the sake of it, but this is not the case, or at least highly unlikely. Bipartisanship is always a means to an end. Many people say that end is a "common good," they want to achieve. In the political climate of 2/21/2018, it means gun control. It means both parties coming together to say "we want fewer school shootings." Regardless of the validity of the argument, that's what it would look like. So why are there so few Republicans (who may be bipartisan on many other things) willing to sign on to gun control legislation? Because what those Republicans value is re election, and voting for gun control will not get them re elected. If they valued "bipartisanship" and the "common good" in so many other instances, why won't they do it now? The answer is they don't value bipartisanship. Not as much as many, many other things that come first.
This is not exclusive to Republicans or gun control or to the United States. Bipartisanship is a farce anywhere. People are always going to do what they can to get what they value most. They might use bipartisanship to get those things that they want (gun control, universal healthcare, immigration reform etc.) But it is strictly a means to an end, not an end in itself.