You are inferring that "all" wild snakes would eat if they can find food. Unfortunately there is no way to prove that. I will grant that generally it is a result of husbandry but there could be undiagnosed health issues but since we would have do a necropsy on the non-eaters to prove that. Not likely to happen. I am a believer that just because we find something that seems to work that we should stop looking for something better.