It’s a story as old as D&D itself. A player doesn’t like their character—these things happen!—and decides to play a new one. But instead of a pleasant retirement, the old character suffers a drastic and terminal end. Methods vary from self-inflicted injury to lurid player-narrated tales to the time-honored “death by goblin,” where the character is thrown into deadly situations until the dice take their grim toll.
Why suicide instead of peaceful retirement? There are, I think, three reasons:
1) The Reroll: By the book, if you don’t like your character’s stats, you can’t reroll. You have to play the character you rolled. Character death provides an end run around the problem! Just view your replacement character as your “reroll.”
2) Player Authority: In a world where the DM controls everything other than your character, you may feel that surrendering control of your character is anathema. Killing your character is a final gesture of defiance in the face of the DM’s implicit tyranny.
3) Closure. What’s the end of your character’s story? If the character recedes into the quiet mists of NPCdom, you may never find out! Better, perhaps, to write your own ending to the story while you still have authority to do so.
Personally, as a DM, I find it annoying when players casually kill off their PCs. Characters in which the group is emotionally invested are valuable assets to the DM, and I hate to see such assets tossed away thoughtlessly or inefficiently. On the other hand, I can see how players can find such an attitude grating. This tells me that this is one of those things that should be talked out between players and their DM.
The important thing is that if you’re going to wipe the slate clean of old characters, that you incorporate it into the story of play just as you would everything else. Adventuring is a ghastly profession. Does it drive people to suicide? Does it welcome those with a death wish? Is it a magnet for character-killing weirdness? Of course!