For career driven people, it's not enough that just some company will hire them for something. And there are very few cities where it's easy to find a job matching the skills and expertise of e.g. a Microsoft tech lead.
You can be a Microsoft tech lead in Raleigh-Durham, too, but you aren't going to have as many opportunities with Amazon/Facebook/Google/etc there.
Actually, I doubt that Microsoft tech leads are as special as all that.