I think the difference is with food you have to eat it. You don't need alcohol, opioids or nicotine to live. With food it's much easier to fall back into similar or the same pattern as before because you can't avoid it.
Chemical dependency I believe can confuse the brain, where it actually does think you need the drug to live.
It can be very hard to avoid booze or cigarettes. They are everywhere. Potentially throughout all of a person's social group. Maybe at home if spouse or parents smoke.
As a former smoker, changing diet was easier for me than to change a smoking habit
The other problem being the availability of healthy food. Those without the time or facility to cook are dependent upon stores selling convenience foods which are anything but healthy, those foods labelled as such being some of the worst examples.
Despite not being overweight and taking regular exercise, I have recently been diagnosed as diabetic and now see the world in a different light. It really is quite shocking how many aisles in. a typical supermarket are stocked with complete junk food.