because its funny. we can all laugh our asses off because we've accepted the fact that skiing could kill us at any momeny. one wrong move and we've smashed ourselves into something. its the same reason why you can heckle people from the chairlift if theyve fallen.
and besides, the funniest things in the world are the most twisted and intense, theyre just not funny on a traditional "haha" level. just laugh and be happy its not you.