People are not always rational utility maximizers. See the Ultimatum Game[1]. There are always people who would rather get nothing than get a small amount when they know the other person would get more.

1: https://en.wikipedia.org/wiki/Ultimatum_game

Assuming a game is played more than once (a safe assumption for human social behavior), I think an occasional Defect / Nobody Gets Anything is quite rational: it's a credible deterrent to disincentivize a grossly unfair distribution.