My logic:
1. Hips fail at a greater rate than knees, period. In other words, your X% likelihood of an eventual hip replacement is higher than your Y% likelihood of a knee replacement, regardless of lifestyle.
2. Distance running attracts obsessive folks who train through injuries and possibly more than what’s advisable as they age.
Put 1 and 2 together, and you have a cohort that excessively stresses the joint that’s already more likely to fail. Add in the percentage of runners with poor diet habits (you can have inflammation without carrying excess weight) who eat crap because they can, lack of proper cross training to offset pounding the concrete, etc,. and yes, you have a higher ratio of runners vs. sedentary people with hip arthritis.