It might be anecdotal, but I run and bike because I've never been good in most popular team sports, such as basketball, soccer etc. On the other hand, running, biking or swimming do not require social skills, dexterity or other skills associated with the more popular spots. As long as you know how to run, it's just a matter of stubbornness/discipline. Plus running is a blessing for those who prefer peaceful activities. You get to run alone in the woods.

Friends who are programmers or who have white-collar jobs are in similar cases (were good/great in school but were last in sports classes)