Which is why Bernie was called the amendment king? Because he accomplished little to nothing? Also Bernie didn't seek out attention nor did AOC; the media came to them, and of course they're going to use the platform to advance an agenda they obviously feel passionately about, as well they should.
Sadly, the advantage overwhelmingly lies with establishment candidates who at present have commanding leads in terms of their resources, party contacts, and the like and moreover typically enjoy leads in terms of incumbency, name recognition (particularly since most progressive candidates are completely new) and media exposure/favourability (anyone who thinks the MSM is enamoured of progs over 'centrist' Dems clearly hasn't been paying attention). I don't think one mid term is at all meaningful with respect to judging the trajectory and health of a movement that only really came into existence 2 years ago vs a faction that has existed for dozens of years now and still holds the majority of the power and purse strings; as a basis of comparison, it took the New Dems about 15 years more or less, to convincingly take over the party, and that was with the backing of big donors unchained by Buckley v Valeo. In light of that, progressives had a great year, particularly when you consider, due to their tireless work, the broad-based, even overwhelming majoritarian support for their keystone policies that are now very much indeed beginning to enter the realm of political possibility, contrary to your increasingly baseless opinion.
I don't see an explanation so much as a self-serving gloss over of Crowley's substantial funding advantage, name recognition, incumbency, party connections, media coverage and so on. Her win was considered an upset for good reason, even if you would like to engage in revisionism to marginalize it as so many centrist Democrats tried to after they finished collecting their jaws from the floor; Pelosi's flailing, ridiculous attempt at minimization was especially hilarious.
