One problem may be that Sanders has no heir apparent.

[Gothmog]

26. Sanders's secret is out: He has no movement - The Washington Post

I have never taken sanders seriously as a candidate due to sanders complete and utter lack of legislative accomplishments. sanders has not been able to get his fellow Democratic members of Congress to back his agenda and that is not going to change. As I understand it, sanders is now relying on a magical voter revolution to convince republicans to be reasonable. sanders has no magical voter revolution or movement backing him up. sanders has a cap of around 30% of the Democratic voters and that does not constitute a movement or revolution

Link to tweet

For months — for years, really — the media have reported that the Democratic Party has gone far left. They have treated social media as a barometer of the party’s political attitudes and characterized center-left candidates as out of touch with their own party. They have done so despite the triumph of moderate Democratic House candidates in 2018; despite the failure of left-wing Democrats to flip a single House seat; despite the polls showing a substantial percentage of Democrats consider themselves moderate or somewhat liberal; and despite the failure of super-progressive presidential candidates to attract the most critical element in the Democratic Party (African Americans).

With this faulty premise, the media’s coverage has been at times wildly off-kilter. It was easy for anyone caring to look closely to see that Sen. Bernie Sanders (I-Vt.) did not “win” a single debate, because his ranting and raving merely reinforced the fervor of his own cult while turning off the rest of the party. The media have been obsessed with the “likability” of female candidates, never considering that Sanders’s angry and rude demeanor would turn off women, who make up more than half of the Democratic electorate. A simple question — “Who is he gaining by all this yelling?” — should have been front and center in the media’s coverage. His “movement” was assumed but never examined carefully.....

Sanders’s ceiling turned out to be real, because there are generally less than a third of voters in the Democratic Party willing to embrace wide-eyed socialism, venom-filled rhetoric and utter disregard for the demands of governing (e.g. compromise). Michael Moore does not speak for the Democratic Party any more than Rep. Alexandria Ocasio-Cortez (D-N.Y.) speaks for House Democrats. (I have long maintained that the person who has the best read on the party as a whole is House Speaker Nancy Pelosi; get to her left, and you are in no-man’s land.)

The Democratic Party does not live on social media nor does it favor bomb-throwers. If anything, it is desperate to play it safe and find an antidote to President Trump — not an imitation. Voters want the madness, the cruelty, the dysfunction and the stupidity to stop. They have found their safe, reliable and decent candidate in Biden. En masse — in every geographic region and Democratic group — they are telling us that they want the primary to end and the effort to rout Trump to begin. The media might have taken Sanders’s “revolution” seriously, but it turns out that Democratic voters as a whole did not.