From the outside, it seems like Canary Warf was where most of the high density building in London was done. That wasn't nearby lots of low rise single family homes, was it?

Certainly, some people are moving to the Bay Area, but the rate of home building well exceeds the population growth rate of California (or England) which are occasionally negative. It's mostly a question of new people wanting to move to particular places they like. But ask, why do they like them, and how was that created? Also ask, what fraction of the residential homes are occupied. In California (especially in desirable areas), the answer to that is likely <90%. Nobody (especially not developers) want to raise taxes on empty houses/apartment/condos/retail, but maybe it would fill up if they did (and lower prices for people who want to rent/move in.