It assumes that Pete's support will be divided pretty evenly between the top 4-5 candidates. But getting an extra 1-3% is quite helpful to Warren and Bloomberg, who are very much flirting with 15% in many places. It's somewhat helpful to Biden, who under 15% in some places.
Conversely, Bernie was already at almost 15% almost everywhere. So picking up his share of the Buttigieg vote, and he probably will get his share, doesn't help him as much re: the delegate math.
Of course none of this accounts for the real world context in which Buttigieg dropped out, in which it may be read as a signal by his voters that they should go to Biden. Our model is a simplification and there is likely upside for Biden vs our projections.
