this seems way too simple to actually be reflective of the truth, but it underscores a concept of groupthink in the party base. the media is talking about things like "electability" and pointing to polls about the topic, but this is a kind of entrapment leading to what i think is probably a strawman: you asked them that (leading) question so you could say that. you didn't ask them about tribalism in the party.

there's no reason to think this is permanent. granted. but, it indicates that democrats may just not really want to deal with a lengthy primary - that they want continuity, unity and a common front. this isn't necessarily about "electability", but may actually be about hierarchy, and a desire to put the party first. it may be a kind of corporatism, or collectivism, that is about subsuming the interests of the individual into the interests of the collective; people might just not want to cause a ruckus, right now. in that analysis, biden is leading because he's seen as legitimate; he's the rightful heir, whereas bernie is a distant second in succession, and the rest of the field are upstarts and pretenders.

under that reading, perhaps sanders was ahead in the polls because the media told voters that sanders was ahead in the polls. and, perhaps biden is now ahead for the same reason.

if the base is interested in a policy discussion, that could change. if it isn't, it might not - and bernie needs to get out and register.