It's not the American ideal of a completely private, individual house/apartment. Living with roommates is seen as subpar or not a good choice for an adult.

I see what you mean. I've been moving quite a bit last few years, and the biggest factor that's prevented me from moving into a shared living spaces is my physical belongings. It's difficult moving a small apartment worth of items into an already established home. Or otherwise, establish a place and find renters with a complimentary set of belongings. I suppose practicing minimalism would get facilitate this.

Well if you want stuff, you have to pay to have it. We falsely think that acquiring things is a one-time cost. While true that owning something typically has a lower total cost of ownership, the relationship is not as cut and dry as often made out. For most people, renting certain things that they currently own would be a better use of resources.