> ...it's expected quality of life that makes people move to NYC for work and makes dilapidated areas unattractive.

I can't speak to Britain, but in the U.S. there are more people that do not live in SF or NYC than do. Other than people with niche interests (musical theater, startups, finance), most Americans, even young adults, aren't sitting around wondering how they can swing a big move to New York City.

It's much more normal to move to a regional big city, but in those cases the jobs are likely outside the city center as downtown. It's worth noting that NY and California would be stagnating if it weren't for immigration. Immigrants seem to be the ones who see places like SF and NYC as their big chance for a new quality of life.

I'm not sure about that, take a look at any of the who's hiring threads and note how nearly all the UK jobs are in London.

Yes because London is best for the Founders, VC, Investors, Board of Directors and C level executives. Not because it is best for employees.