Because the Evening Standard has been reporting in a survey which rates it at the worst place in the UK
www.standard.co.uk/news/london/london-named-worst-city-in-the-uk-to-raise-children-a3539611.html
Main reasons are house prices and crime rates. The other factors they considered were access to green spaces, school rankings and average salaries. Not sure if they included other things, or how they weighted them.
Somewhat to my surprise, it said the best part of London to live in is Peckham. (or am I just hopelessly out of date?)