People in tech want to be in the Bay Area because the most intellectually, emotionally, and financially rewarding tech jobs are concentrated here.
Although some are also scattered around the country and the world, the job-hopping nature of our industry makes it a really bad idea to put down roots in a one-company town. Places (Seattle, Portland, Denver, etc) which begin to mirror the Bay Area in terms of tech employment opportunities start to look like it in terms of housing and traffic, too.
I'd wager that almost no SF tech worker choose it for the city first and job market second. Personally, I'd love to try being rural and remote, but I've yet to hear of a remote job that I'd be similarly interested in and passionate about, much less one that would pay comparably.