Hobbies aren't necessarily only relevant to oneself, so no, they don't fit. Running a marathon can be a hobby, and lots of people compete in those together.

Not necessarily, but more often so than not. Even the competitions that you mention are only valuable to other hobbyists, and only in so far people's free times allow. Non-hobbyists are not likely to pay much to see those competitions. And when free time runs out, those hobbies are amongst the first things to go.