Some of the echo-chamber is tribal signaling: "I'm one of you: see, I don't even listen to the bad tribe!" Wanting to be a member of a tribe is a good thing, but we all know how badly that urge gets misused.
There's another factor: "Leave the presence of a fool, or you will not discern words of knowledge." (Prov 14:7). If you hang around fools, you will waste your scarce minutes and brainpower with foolishness, and have to unclutter your mind again to be able to receive wisdom. I'd take that verse to be a directive to avoid TV, but I could also take it to apply to avoiding sloganeers. Since sloganeers seem to be a majority of the people speaking for a particular party, it is only a short step from there to avoiding listening to anybody speaking for that party.