It's the same as with any activity.
- A lot of the decide they have gotten too old for it.
- Some people develop injuries that make it challenging to continue.
- People get a "been there; done that" attitude toward activities after a while.
- People start a new activity that draws their interest and leaves them less time for a former activity.
- Personal life issues get in the way (raising a family, moving for a new job, etc.)
For many it is a combination of the above. Here is a short autobiography:
- I was once an avid photographer, with a high quality camera, multiple lenses, and my own darkroom. Today my wife has to push me to take pictures with my iPhone.
- I coached high school basketball for 14 years. I coached in state championship games, and I was once selected to coach the state all-star game in the summer. I haven't watched a basketball game at any level in many years. I can't tell you who won the NCAA or NBA championships in the last decade.
- I had an "A" ranking in doubles volleyball, meaning I could not compete in "B" level tournaments. I preferred 6-man volleyball. I was an official with the professional volleyball league. I have not touched a volleyball in decades, and when I see a 6-man game today, I see that I don't even know the rules any more.
- I played a lot of tennis in my day. That ended with knee replacement. I have not owned a racket in 15 years.
- I was an avid skier, and I even competed in races. Knee replacement ended that as well.
At my age (72), it would not surprise me if diving came to the same conclusion. If it does, I will find something else to replace it, and I won't look back.