I think the struggle is that while the party and establishment dems that run it are basically republican lite. A lot of people still in the party, who don't fit or agree with the establishment, haven't come, for whatever reason, to the realization that that is what the democratic party has become.

I think for some it's a laziness issue. For others it's not having enough resources to understand. And for some it's probably a hesitancy to no longer ally with a party they have long been a part of. In the US, parties tend to be like factions that people dedicate to instead of a means to a political end.

Also most Americans still think left and liberal are the same thing. So there's that hurdle too.