Many cities many EAs live in have very high living costs. Thus, even full-time working adults often do flat sharing. This is why some people have set up EA (or rationalist) group houses: they’d prefer to live with like-minded folks.
This is only partially true. There are many EAs living in group houses who could afford to live alone but prefer group houses.
Also, the Bay Area is probably the top metro area in the world for AI capabilities R&D (because of Google, OpenAI, Meta, various ex-Brain startups, Stanford, Berkeley). So if starting from scratch, there’d be a good reason to put AI Safety orgs there.