There are a couple of problems with docs and Basic Med
Insurance usually doesn't cover something like a Basic Med exam. It's kind of like a scuba clearance or DOT physical. It's not required for your health, which is why insurance doesn't cover it. It's either for your occupation, so in theory your employer should foot the bill, or recreation, where, well, you foot the bill. A lot of doc's don't like dealing with these kind of non covered extras. 600 is too steep. But if you think that a decent lawyer nowadays is $400 hr(am I paying too much

), and that a halfway thorough Basic Med evaluation would be 20-30 minutes of history and physical and 5-10 minutes of paperwork time, a charge of ~200-300 isn't all that unreasonable since insurance covers nothing. As a courtesy, some docs would just do it during a regular physical and absorb the cost, but...
The pesky liability question, combined with the average doc's having no clue about what makes someone "safe" or "not safe" to fly. We all knew in medical school that, if you wanted an aviation physical, you went to an FAA doc, so to speak, someone with extra training. The issue never came up. And then congress came a long and said your doctor can sign this form stating whether it's safe to fly or not and legally attest to this.
Subsequently all of us docs just kinda looked at each other in a great big imaginary noon lunch meeting and muttered to each other, "WTF does this mean..." Especially since, at the end of the Basic Med exam form, right above where the doc signs, is the attestation that, essentially, the doc finds the patient fit to fly. The average doc isn't taught squat about aviation medicine.
When congress cooked up Basic Med, it appears they didn't ask the FAA much, which was probably good. The problem was that it appears congress didn't ask practicing doctors what they thought either. You and I understand Basic Med, but the average non-pilot doc doesn't know anything about it, unless he or she goes out of his way to learn. Until I got into aviation, I didn't know anything about aviation medicine/Basic Med. I don't know if the average malpractice carrier actually has rules against signing this kind of form, but I will say that, depending on where a doc works, and perhaps which malpractice carrier he or she has, there is some "pressure" and "recommendations" not to sign these forms...
Congress could have put in some basic protections for docs, a "good faith clause," etc that at least shielded a doc at least partly. I'm sure the lawyers, i.e. most of congress, doesn't generally like this idea. But, if you want to encourage a group to do something (i.e. get your doc to sign a Basic Med form) then offering at least some limited protection from negative consequences might be helpful.
If the average doc doesn't know anything about aviation medicine, isn't well compensated for a Basic Med exam, and is exposed to liability, well, not surprising that we're not all clamoring to do Basic Med exams...
So, it appears, for the time being, finding a Basic Med doc is going to be a bit spotty.
FWIW my internist doesn't do them either so I found a local chiropractor who does them. Yeah, so, not sure the system is working exactly as intended...