I never understand why people (especially in the US) have a desire to split everything into two opposing sides. Liberal/conservative, introvert/extrovert and many others. I think it's pretty obvious that most (all?) people are on a spectrum of many dimensions and can't be categorized that easily. These labels can give useful hints but there is way more detail to look at.
Fundamentally, this is a typical strategy for the human mind and even organisms in general, to understand the world by categorizing it into opposing pairs: light/dark, hot/cold, life/death, up/down, left/right. This is often discussed in Buddhism, for example, there is a whole school of tradition called "Not Two" that focuses on going beyond this illusion of duality.
About how polar opposition seems to be stronger in the U.S., in my opinion that's due to the weaponization of culture in the country, how the media is used to manipulate the public into outrage and conflict. It's a form of social control that's pretty much everywhere, but it seems to have especially reached a boiling point in the U.S. in recent years.
It's a primitive, simplistic and reductive way of looking at the world, ignoring the spectrum in between the opposing sides, which are arbitrary anyway.
Maybe there are introverts, extroverts, various mixtures between, and even hyperverts or transverts who prefer one side or the other depending on their mood or life stages.