To be honest I think it’s because obesity doesn’t operate at the same speed as drugs/alcohol. It does similar things to your body in terms of addiction, but if you were to put down the needle or bottle for a few days there would be a very quick and clear change, whereas obesity takes longer to come down from. Like you can tell if an alcoholic is a mean person or just a mean drunk as there are short periods where they’re sober, but there’s no human period for obeasts where you can see that stark difference. They’re just “high” all the time, and humans are really bad at seeing changes over longer periods of time