I think there are two different things being discussed. Dormmates and apartment/flatmates.
I can answer for the University of Texas dorms which are pretty standard. The dorms (most of them) are owned by the University. You apply for a space in the dorm of your choice. There are single, double, and triple rooms. The more people in the room, the cheaper the per person cost. If you have a friend you want to room with, they will do their best to accommodate you. But, yes, you can be assigned a complete stranger to share a room with. Bathrooms might be shared in a suite of two or three rooms. OR they might be communal showers for the hall/wing.
The US used to have single room dorms as a rule before WWI like the rest of the world. During WWI, flight and radio schools sprang up on college campuses. After WWI, people who hadn’t ever considered college before began enrolling. Lack of dorm space meant doubling up. Eventually, that became the standard rather than the exception since so many were trying to keep college costs down.
For apartments, you chose who to live with. Two people sharing an apartment can afford more space with better amenities. If we’re talking college age students, four students may share a two bedroom apartment sleeping two to a room to keep costs down. Post college, it’s very rare to find two people platonically sharing a single room. Right out of college, many people continue having a roommate for money reasons or because they feel lonely living alone. I have a co-worker who has a platonic roommate. He can afford a better apartment with a roommate than he could on his own. He’s in his twenties. It’s not the norm, but it’s not unheard of for a professional several years out of college.
Austin is expensive. $1250 a month is the median for a one bedroom apartment. So lots of people with lower paying jobs pretty much have to have roommates.
:rolleyes: and immediately left. The next guy who looked at it had roommates before and suggested that we talk with the landlord about renting a two bedroom. There just happened to be a 2 BDR opening up down the hall, so we shared the flat there.