Any able-bodied person who owns shoes can run. Even people too poor to own shoes can often become excellent runners. Coaches help, but many people have reached near elite levels before having access to a coach.

It's the one sport that's open to just about everyone.

Perversely, this makes its highest levels open to only the most extreme of genetic freaks.

You need a lot more than shoes to run a marathon. The time and environment required to get there is much less accessible than something like soccer, football, or basketball.

You don't even need the shoes in all cases:

> "Many theories are offered up as the secret to Kenya's success in long distance running, but one of the most commonly cited, especially by Kenyans themselves, is the hard, active life the children here lead. Most run long distances to school each morning, and when they get home they are sent out to tend to the goats or sheep. There are few televisions, let alone PlayStations or Xboxes."

https://www.npr.org/sections/goatsandsoda/2014/11/04/3614032...

It's definitely true that the marathon is somewhat less accessible than short or mid-distance running, but it doesn't take years of marathon running to be a top marathoner. Much of the fitness transfers from mid-distances. Many competitive 10k runners post elite times in their very first marathon race. This means that in practice, the marathon is very nearly as competitive as that for a middle distance race.