Pelosi is part of that cabal that sold out back in the Clinton era to the Wall Street lobby and never looked back. All they care about deep down is staying in power and boosting their party otherwise they'd show some real leadership.
What they're terrified of is a third party capitalizing on everyone's angst at D.C. national approval ratings for Congress hover in the low-30s at best most of the time. Only the fact that there's no alternative identity with broad appeal to rally around keeps the Dems from fragmenting and they know it.
The political realignment that *should* happen is both parties split, the few sane moderate GOPers join the corporate Dems while the wings jump off to be regional opposition groups.
But nobody wants to take the risk they'll wind up being screwed in the process. The country is still limping along, why change now when your entire leadership caste is 80 and not likely to experience the consequences of their lack of vision for very long, if ever?