Apologies for the broad generalization (as I said, correct me if I'm wrong, and I stand corrected here). That being said, if what you say is true, it's a pity that either the main stream media's reporting doesn't reflect that diversity or that the louder voices don't leave space for the rest of viewpoints.
With the rise of Bernie Sanders and a new generation of people getting into socialist and left wing politics, it became quite a bit broader and larger and vibrant. And my impression is it became of a centre of gravity for other left tendencies in the US to coalesce.
There's quite a few different groupings in there these days. I don't think you can make a broad generalization like you did here.