Completely off the subject of AC: Why doesn't your "group" of neurologists for a separate company that you each own a piece of? That would be the header name such as "Smartest Neurologists in the Western Hemisphere". It would also provide a company that you each own a 3rd of to pay shard employees, shared equipment, lease payments, etc. You then each have your own "S" corporation as your self (i.e. NeuroDawg, M.D., PA) to buy your own personal equipment or pay your personal nurse, etc.
Anyway, this is way off the subject but if you guys aren't doing that, it really helps come tax season.
Habit. It's how the other two were doing things long before I joined them. And one is close to retirement and I think is a little afraid of being a "co-owner" in a limited partnership or corporation. Our bookkeeper and CPA has been dealing with it for years, and our CPA and financial advisors tell us there's no advantage to doing so, that when all is said and done, it's a wash; same costs either way.