When I was moving to the South Bay and had only two weeks to figure out my plan, can't tell you how many somewhat affordable room rentals in non-luxury apartments had crazier setups.
Some of my favorites: 1. Spacious open room with bed (it was someone's garage with a sheet down and a mattress on top of the concrete)
2. Pretty common: nice place but you were not allowed to use the kitchen
3. Converted Living Room (no joke, the photo was a twin bed in a living room with Office Depot boxes to create a divider)
So yeah, I get why someone would share a room in exchange for having some amenities.