I believe that most people quit going to the gym because they get bored.
So if there were an app that takes several factors into consideration¹ and generates workouts for them, and that would change it up, people would stay interested and gain fitness.
Which works against the business model of many of the chain gyms -- they actually want people signed to yearly contracts that then don't show up.
¹ Perhaps it would consider available equipment, desires of the person (some ratio between speed/endurance/strength/stability), when they last did an exercise, what their feedback was from previously doing it, what muscle group it most effectively works, what the opposing muscles are and when they got worked, and so on.
