It's cheap relative to most other sports/exercise. If you do the same analysis (you've done it to make this story more substantive) for another sport you will see.
I'm avid runner. The privilege of living in California aside (year around running), all you need is ... running shoes. I have 3 pairs for different types of training. Let's say I need to renew them once every for month because they wear out. $150 per pair, so $450 per quarter, $1400 per year. I guess indeed not as cheap as sometimes claimed. However, I run 70 miles a week. Most people run a fraction of that. So ... all you need is a pair of running shoes. So accessible