Let me answer by recounting the experience of my oldest daughter who, after graduating from college, moved to Jackson Hole, Wyoming, which is not affordable by conventional metrics (though probably not a bad as SF or NYC). She shared a little apartment with three other roommates. They periodically had friends who would crash and sleep for weeks on end on the living room sofa. Young people don’t have the same expectation of living space and privacy, therefore, they are willing to economize on rent in a way they would not tolerate once they were married and had children.