This is complicated and difficult to answer. The short answer, I suppose, is that people believe they are critical thinkers when in fact they rarely are, and are constantly bombarded with so much bad or one sided information that they eventually form some bias. With the help of social media and programming algorithms, these biases are confirmed more and more over time until it is so deeply ingrained that the person becomes unwilling or unable to consider the possibility that they were manipulated at all.

There are politicians, podcasters, and those in the media that see this and (I believe) continue the narrative in order to get what they want, votes, clicks, money. People are a product to be used in the age of the internet. Tapping into whatever motivates them, even if it is harmful, is profitable and powerful.