Because - like Bin Laden - he's one of those evil guys that everyone hates and wants him to get what he had coming to him - justice wise or not; whether that be a law precident punishment or the chance for every person to punch his nose to the back of his head.
It's more fitting balance and justice wise for someone to get the punishment they deserve for their actions rather than for them to take the easy way out and kill themselves - almost cheating in a way
Also I believe he went back and tried to kill Hitler back early during World War I...the pathetic part more evoking the dilemma of "to kill someone who will do something bad in the future" paradigm. Had the guy been sent back to during World War II times - he'd appear much less pathetic and much more deserving of what he was getting