It's just the way some people are wired, and sometimes peoples' wiring changes. They may decide they're not comfortable with the idea of someone else being able to do something they can't. They may have always wanted to climb the highest mountain in the world. They may just want to add it to their summit collection. Sometimes it's just a job. Sometimes it's a trophy, or the crowning achievement of a lifetime.

I used to have arguments with one of my old roommates about space exploration. He would argue that if we found a planet several thousand light years away that could support human life, we'd never get there because nobody would volunteer to go. I could never get through to him that there are people who will take any risk to get to do something like that, even if it meant only being memorialized in the memories of their distant descendants or being frozen for a few thousand years and never again seeing everything they'd ever known.

However, human history supports the idea that there will always be those few who are willing to do things for reasons which evade the rest of the human race. That's just the way we're wired.