I would assume that physicians have the basic knowledge of patient safety in terms of surgical risks. Saving the patient thousands of dollars would not be worthwhile if it meant putting the life of the patient at risk. Probably it would mean he is putting his practice at risk as well (like a lawsuit). Like you said there is a reason why a certain procedure or surgery needs to be done in the OR. One reason that comes to mind is that the hospital has the correct medical equipment/supplies and clinical manpower should the patient experience a surgical complication that is emergent and life-threatening.
I'm wondering if the ENT physician is performing procedures that would normally be done in an ASC setting or in the hospital-based outpatient department setting, how he can even get paid appropriately for his services.
Perhaps, you can help to educate the ENT physician by using materials from legit sources such as your state's laws. For example, I found this document regarding office-based surgery on Oregon.gov: https://www.oregon.gov/omb/Topics-of-Interest/Pages/Office-Based-Surgery-Proposed-Rules.aspx. There is a wealth of free information on the internet (and printed materials) and putting together a coherent material that only contains information from valid sources is one inexpensive thing that can be done. Just my personal thoughts.