They do "care".

First of all, if that number is in the interval [0,1], it's a qualitatively different situation than if the number is in [2,∞].

Jokes aside, there is a statistical relationship between the number of people in a room and the distance they can/will keep from each other. More density means more close encounters on average. Less density doesn't guarantee nobody gets too close to someone else, but it makes it less likely.