For game jams it seem to be the one contributor that has rated the most. That would mean that if all contributors play random games (and comment feedback which will in turn spread the game) it would be hard to get a high karma. If I am in a team of 3 and we play 10 games each we get 10 coolness from 30 ratings. If everyone that we rated gives ratings back, our karma wouldn't be as good especially compared to a solo dev that rated 10 games and got 10 back.
I am not totally sure if this is the case but it seems to be accurate when looking at https://itchanalytics.vercel.app/ and comparing to how many rating my collaborators have done. The one with the highest is the coolness value we currently have.