Re: the above problems point to one root cause
Because the entire point of an office block is to be near other office blocks.
This allows the high-ups to think that they are important because they have an office near the offices of %BIG_FIRM%, despite said firm not being a customer or supplier.
This isn't true. It's actually because most companies can only afford one location and don't like the idea of working from home.
Couple that with the fact that people generally don't like to move home, and you end up with large central blocks of "workplaces" where hundreds of employers exist, surrounded at a distance by homes.
Or a "city".