I know someone with type II diabetes, and her doctor prescribes D2, not D3. I've never got her to explain why, but it's the doctor's plan and she's not questioning it.
I had a patient last week whose doctor from the VA (Veterans Affairs) prescribed D2. I told him D3 was much better but it also needed cofactors.
I think most of the prescriptions for vitamin D here in the states are for D2. D2 is less effective at raising vitamin D levels and has a shorter duration of action. And now we know calcifediol is even better but is blacklisted in the USA and Canada!