As others have pointed out, HIPPA is meant to give you, the patient, rights over access to your files. So what if the doctor is uncomfortable sharing access? They're your files.

The insurer has a right to request those files if you want your claim to be honored. You're not required to purchase insurance. By purchasing insurance, you acknolwedge that you may have to grant access to private information if you wish to support your claim. So the insurer doesn't have automatic acess to the files (you control that under HIPPA) but it doesn't have to cooperate any further if you refuse it access.