In order of occurrence, starting with the smart-alecky and moving into the actually thoughtful (but still probably seen as trollish): 1) From BASE jumping. 2)

In order of occurrence, starting with the smart-alecky and moving into the actually thoughtful (but still probably seen as trollish): 1) From BASE jumping. 2) For no reason. 3) From incomplete cognitive development (risk assessment, awareness of one's mortality etc.) 4) Because the world economy is sufficiently developed to keep them alive long enough to die this type of optional/discretionary death.