By "most people" you mean mostly 20-somethings? It's hard to imagine people in their 30s and older, married and starting to have kids, living like that. I mean, great if you can pull it off, but you'd have to stagger the shower schedule not to mention maybe get a 2nd refrigerator?
That's not uncommon in London, especially amongst immigrants from Eastern Europe — it makes sense, if the aim is to save money rapidly to put a deposit on a house in Poland/Romania etc — and people in their 20s.
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.
This is the bigger problem. Companies like Google & Salesforce have been there long enough for their early hires to have grown up and gotten ready to lay down roots ... but they can't afford to buy a house and they don't want to raise a family in a small/crappy/inconvenient apartment or condo.
