You'd be surprised how attached people are to their spouses or partners. Doesn't matter how badly you want to work at Google, if your spouse is an IP attorney or VP at an academic hospital, as a family you just can't go moving to the middle of nowhere. It's not ALL about being able to work at Google. There's a lot more going on in making these decisions. (At least there is for the type of people that Google would be interested in.)
Much better to be in that NYC-Boston-DC corridor where high powered opportunities abound in multiple sectors. Or SF. Or Chicago. Etc. But trying to move a lot of these types of couples to, say, Lincoln Nebraska, is just asking for trouble. The spouses or partners are definitely not going to go for that.