Buttboy is picking up some votes from the ones who dropped out, he's likely also picking up warren people as she has fallen.
What's also happening is that the media is overrecting to polls in a couple early states that are not at all like the rest of national democratic party. Buttigiege is more popular in iowa and NH for obvious reasons,(few minorities, more moderate dems). it's going to be really hard for the democratic party to ever rally around whomever comes out on top, 70% dont want biden, 1/2 dont want a socailist. buttigeiege has the gay thing with blacks.
And then you have Hillary, who is almost certain to jump in and really fuck things up, she could easily poll ahead of all the rest, but 1/2 of dems cant stand her anymore than the rest of america.
Trump will be unbeatable.