There’s a conspiracy theory making the rounds. It claims Buttigieg, Klobuchar, and Bloomberg dropping out while Warren stays in is evidence of a DNC cabal to help Biden and torpedo Sanders.
Warren is the one whose voters might be most tempted to join Team Bernie if she quit. The other three’s supporters are viewed as having Biden as their second choice. Or so the theory goes.
Warren will take a reputational hit if she stays in the race past the point where her chances look feasible. Perhaps the DNC has offered to make her doing so worthwhile in some non-obvious fashion - a future ambassadorship or court appointment?