I took a room for ~9 months in what was originally a 3 bedroom house. It was (a) very flexible regarding the contract (b) very cheap (£400/mth). (I had to move out of my previous place, but was looking for a new job, so didn't want to commit to something that might be in an inconvenient area.)
I had my own room, and for most of the time there were 4 people in the three other rooms, age 30-40s and one at 50.
Everyone apart from me worked in the kind of jobs where you have to be in by 7-8am, so I never had an issue taking a shower. We had 2 fridges.
This was a "nice" house, in a nice area, with nothing dodgy about the contract / rent etc. In other areas there are really scummy landlords overcharging people for individual rooms, often none of them are British / western European, so they don't seem to know that there are regulations in their favour, for example for getting a deposit returned, or not paying for wear-and-tear repairs.
Citation required. None of my post-college friends are sharing a room (though many do share their apartment). Yes, rent is high, but it's not that high when compared to dev salaries.
This is skewed if all your friends are devs. The sentiment is true to my experience as far as my non-dev friends go. Many share rooms with strangers or live with their significant other.