A lot of people (I'd hazard to say most people) don't own their own practices any more. Many are either employed by a hospital, a large health system like Kaiser or the VA/federal gov't, or belong to large group practices with a bunch of docs in them, or are employees of large groups like that. The economics of the one or two doctor practice just doesn't work that well any more, in many cases...you don't bill enough to make as good $ as you would just being an employee of some hospital or large group practice, because so much of your money goes to paying office staff and trying to collect the money owed to you by patients and insurance companies.
It used to be that people would pay money to "buy in" to an established practice, usually after working for the other docs there as an employee for a year or two, but now people are not as inclined to do that, in part because a lot of medical practices may not be making the profits they used to, and patients don't necessarily have the same loyalty to a particular doctor or practice that they once had. In that situation, why would you pay money to "buy in" to a practice? Also, most people finishing residency now have a lot of student loans, and with that much debt they don't really have extra money lying around to "buy in" to an existing practice.
Some docs (like dermatologists, for example) still do run solo practices. To do that you'll need to buy or rent office space, and hire at least one other person to answer your phones and help file insurance claims. That would be a bare minimum medical practice. The one solo derm practice I saw rented office space from a hospital medical arts building, and she employed a RN/nurse and 1 receptionist.
I honestly don't know how a bank would react if a graduating resident went to them wanting a small business loan or something...there are probably lenders who will lend to you, but remember you'd still be on the hook for the money whether your new practice flies vs. not.
