Having a roommate has two purposes, I suppose.

One is freeing up $1-2k of disposable income that you can afford to spend on living in the most desirable place, but maybe would rather not.

Another is to feel less alone. Also, having somebody in the apartment when you're away, who could take care of a delivery or a pet may be important.

The people I know who have roommates do it because they’re cheap and they don’t like being alone. This includes people making $400k+/yr. Even people in 7-figure territory.

They’re pennywise pound foolish types usually tho.