There's a legitimate case that the democrats are weary of some of the economic policies they implemented in the late 1960s through the 1970s which led to runaway inflation. The backlash against this economy created the paleoconservative movement and got Ronald Reagan elected. Economically, 0% unemployment is actually a recipe for disaster:

https://en.wikipedia.org/wiki/Natural_rate_of_unemployment#Phillips_curve

Universal healthcare and welfare are good policies, but there were excesses to fiscal policy in the 1960s-70s, and the only way to Democrats made their way back to the whitehouse was with an entirely new generation/brand of democratic politics under Bill Clinton, which embraced free trade and deregulation (i.e, the "third way"). So far, progressivism has not won in the way that this new brand of liberalism has.

I think progressivism could probably win a couple cycles under the right conditions (such as coming off of the disaster of a 2nd Trump presidency) but I think the backlash would bring us what would effectively be a 3rd Trump presidency