I think part of it too is they can run again, they are young enough. They boosted their name recognition and had decent showings, now they are showing they will go along with the party and build some goodwill with the establishment and pushing more votes towards Biden
For Bernie, Biden, and Warren this is most likely their shots given they are all in their 70s. But it does hurt Sanders given Bloomberg is really the only moderate left and Warren is probably taking more votes from Sanders than Biden, though I think there are some odd dynamics and dislike between Warren and Sanders voters even though they are fairly close policy-wise.
In any case, on Tuesday night we will know a lot more about how the race looks.