I'm not outright trying to be contrarian, but for some older people or people with things like arthritis, foot injuries, hip injuries, etc. walking or running on a treadmill is vastly less painful than walking or running on concrete.
There is absolutely a huge commercialization problem with fitness and health in the western world (and in America in particular), but if going to a climate-controlled gym and getting your steps in on a treadmill or elliptical is what it takes to get you to exercise, I'm all for it.
For the potato chips, that's really sleazy of the gym, but I do want people to know that even if you don't/can't make a bunch of changes to your diet and you don't lose weight, getting exercise of any kind as often as you are able is still a positive thing for your heart and metabolic health. Please don't let being fat, or out of shape, or an inability to overhaul your diet prevent you from doing something positive for your health. Losing weight and keeping it off is really only possible through major lifestyle change, and, for a lot of people, the only sustainable way to make the necessary changes is one at a time.