Companies are (generally speaking) founded by people with type-A "go go go!" personalities, who love to be in the center of large cities with all kinds of hustle and bustle. The kind of people who couldn't even imagine living anywhere else.
That's not to say they're idiots, of course not. But it might be to say that the reasons for placing their company in the center of a large city aren't very rational or well-considered.
The country pumpkins are free to start their own companies, if they like it better there.
And lots of them do. See all the startups in decidedly suburban Silicon Valley. (And yes, I am being a bit snarky here in equating everything outside of cities, be that suburban sprawl or proper countryside.)
That's not to say they're idiots, of course not. But it might be to say that the reasons for placing their company in the center of a large city aren't very rational or well-considered.