The polarization is intentional. If people are busy squabbling amongst themselves about menial things(see: HB2/Bathroom Bill) they won't pay attention to the truly nefarious things that are really going on(removing legislative power from municipalities).
TV, social media, internet, etc drive this. I travel extensively for work and engage people all over the country of varying beliefs and viewpoints. The one thing I notice more than anything else is that people are much, much more reasonable when they are talking to another person, even if they don't agree on politics/religion/etc rather than beholden to these semi-anonymous platforms(like we are using now). The fact is, most people are more than capable of having reasonable discussions and even engaging in reasonable compromises when they don't have these external influences inflaming them. This is the era of unchecked propaganda and lies being spewed from Fox News and MSNBC specifically catered to their audiences and deliberately packaged to inflame the public. The social media platforms use their algorithms to spray polarizing content across your accounts in a sick attempt to make you upset enough to stick around.
But, we also as citizens allow ourselves to be duped by this nonsense. We don't use critical thinking, healthy skepticism and we lean towards being intellectually lazy. The powerful use this tendency, largely just a product of human nature, to distract and divide us while they largely obtain what they want in the shadows.
Far left and far right, it's almost like a circle, they all end up at the same place. If you are an extremist on either side, your messages sound so similar it's scary. If you just change a word or two and it's the same message and it rarely changes, throughout history. And yet we continue to make the same mistakes, over and over and over.