Four or five times a week I work out at a gym. John Glidewell graciously and patiently allows me to workout with him. This is not a new experience. I been involved in exercise programs for over 20 years. Let me note just three reasons.
Some people work out to compete or to prepare for some form of competition.
If you work out at the gym to compete with other people who work out, you will always meet someone who is stronger, bigger, and better developed than you are. Some people work out to feel better about themselves. That has merit. But it also has risk. With age and time, we lose physical ability.