In my experience, it doesn't seem to be a common occurrence. At least, I personally know no one doing that. YMMV, I guess. Also, it seems to me like a very bad idea to do that.
What was the potential harm that was greater than the reward?
It's like, not being obese enough for your insurance company to pay for medical intervention doesn't mean that your weight is optimal enough to enjoy a long retirement.
It’s probably very low in the context of CGM and diabetes as the potentially harmful treatments require prescriptions.
Device prescription requirements are usually due to product labelling and the manufacturers application. There are OTC fingerstick glucometers and CGMs approved.