A lot of people treat politics the same way people root for their favorite sports team - as a zero sum game. That is, in order for them to feel good, their team must win and/or the other team must lose. This sentiment has only increased as the modern world has become more secular (people no longer feeling strongly about their religion) and more global (people no longer feeling strongly about the country they live in.

In addition to that, a lot of people still haven't figured out that the political "teams" have changed and are still clinging to Democrat v. Republican or liberal v. conservative. The real conflict has been the establishment (globalists, interventionists) v. the people (populists).