There's a old saying, "Live Fast And Die Young And Have A Good Looking Corpse" from an old Humphery Bogart movie, that would not be too surprising to say, that these people probably saw the movie or heard the quote.
Then preceded to make it their mantra to live by, but then that may be putting a little too much logic into it, these people could be hovering around the border of being plain and simply crazy.
What they do, no sane person who values their life, would dare contemplate in their to-do list.
Hanging by your arm hundreds of feet in the air, jumping off precarious cliffs, doing backflips on top of a building so you can land on a few inches of a steel beam, and performing feats that make onlookers shake in their boots, is not what a person in control of all their faculties engage in at all.
It could be that these individuals have one thing in common, and that is their, Prefrontal Cortex, is still developing. (you know the part of your brain that makes you feel invulnerable).
Whatever it is, that makes an adrenaline junkie seek out his fix, is for us cowards to sit back, shake and enjoy, and secretly wish we had it in us to be right out there with them.