All good points. I studied sports psychology in college and wrote a paper on this subject. My paper was specifically on rock climbing, but lots of crossover to other sports. There are some arguments as to why rich people are attracted to endurance sports (risk-taking mentality), but there are more arguments as to why low income people don't do it as much. It requires too much mental and physical energy, which low income people do not have a surplus of. They are using that energy just to get by day to day. There have been lots of poor climbers, but mostly that is by choice.