The American left's branding is being "other" to the status quo. Nothing can simultaneously be both status quo and belong to the left. Once something moves from the "left" to "status quo" the success doesn't count, because it's no longer the "left's," it's everybodies. And the left has to find a new way to be against it (or stay silent on the topic).
Without saying anything about where the force vectors that create this common view comes from, the sum result is a narrative with bounds. Bounds that are reinforced and entrenched because they can be useful to leverage for political gain by them and/or their opponents.
So no matter how many times the left have succeed or will succeeded at marketing many ideas to the average American, some people feel they're much more ineffectual than they are.
From feminism, to antifa, to anything touching economics, the American left tends to get itself deep enough into identity politics and neoliberalism to disgust about anyone here (I'm Spanish).
There definitely is something regarding American politics that sets it apart from the European understanding of how politics works, I personally think that the system encouraging a two party system establishes too strong of a "us vs them" mentality and that it damages political discourse altogether.