I've often wondered about this- I mean the US has it's share of coffeehouse anarchists and redistributionists. The large size of the US and the political structure make it hard for e.g. a 'Pirate Party' representative to appear, even if there is the same amount of support per capita.
The implicit premise itself, that the Democratic political party is monolithic is false. It was an old Woodie Alan joke about not belonging to an organized political party and that is true to some extent - if your group is excluded from the GOP the DNC is the big tent. Before the 9/11 xenophobia US muslims were dominantly aligned with the Republican party, afterwards it was reversed. There are in fact many religious conservative demographics in the DNC for one.
Frankly self proclaimed leftists have a terrible habit of consent manufacturing - both from their own natural bubbles and echo chambers and ad nausuem rhetoric. There is tbe "implicit identity and support" which assumes that universal support of the working class is the natural status quo and any who disagree are puppets of the rich. This abstraction spares them from having to consider the actual opinions of the people who compose it. Their poor electoral performance in even their strongholds highlights that they are a noisy minority operating under the pretense of being a majority.