Private offices can solve the headache of a bad co-tenant, but have their own headaches as well. The obvious one is that it's more expensive. A less obvious one is that you loose the access to outside people. If you're working near someone else, it's fairly trivial to go ask them what they think about something. You're likely to talk to them anyway, so it's an easy way to get an outside perspective by someone probably in the same industry. It's a natural form of networking as well. There are certainly benefits to having a private office, but it's not nearly as cut-and-dry as you're implying.