In most other outer boroughs, getting home after midnight is either very expensive (taxi/minicab, including Uber) or very slow (two or more night buses). Most people I know -- in their 20s -- prefer a shared house closer to the centre.
All this will change in September, when (if?) the night tube starts running on Friday and Saturday nights.
[1] https://tfl.gov.uk/cdn/static/cms/documents/tube-dlr-lo-adul...
If the tube ran at night, I could reasonably stay out late in Zone 4+! I can't remember the last time I did that. (Why might I want to? Because people live there, and have BBQs etc.)
It sums up the absurdity of the situation when it's genuinely and routinely proposed that a solution to ridiculous cost of living in a city is to live.. not in the city.