I do think bar for most people "getting their money's worth" from their gym membership is quite low. For example, consider my Dad, age 81. He does walk around the neighborhood with my Mom quite regularly, every day when he's feeling up to it. But he has hip problems and there are other things (like swimming) he can do at the gym that are better for his hip when it's hurting. When you consider the cost of medical care, a $100 / month gym membership is absolutely nothing. If you use that membership twice a month as a senior citizen and reduce your chance of hospitalization by 2%, you're probably more than getting your money's worth. (Hospitalizations run into six figures VERY quickly.)
My Dad is very frugal and is always fretting about spending more than the absolute minimum. But I always tell him that even if he'll use the gym even once a week, it's worth investing in the gym most convenient for him in the city, no matter the price.
But I guess that logic is how people get sucked into unused gym membership.