I would guess marathons select for people trying to push themselves hard, in a short period of training time and for a relatively short period of time. I also wouldn't be surprised if marathon attendance skews upper 40s / low 50s, male, and recently got in shape. That's a bit different than sitting in the desert doing drugs. the risk there would be respiratory distress / fent od is my guess.

it's a lot easier to get someone out of an opioid od in the field than it is out of cardiac arrest, or at least the treatment protocol is.