I think one reason that is often overlooked in that polarization is that there are a lot fewer places in RL too where you have to interact with others in a more than superficial way or even can do so if you actively choose to do so.

A big reason for that is cars which isolate people as they travel from place to place and another is the reshaping of our cities into large homogeneous parts, each just for a group of people with similar income and culture.