I guess I can understand wanting to show off what you've done in a game, and for other people that's fine ("Good on you, you beat it on the highest difficulty without dying even once"), but for me, I love thinking up challenges that the developers didn't suggest you to do of or doing things outside the scope of the game (you know, like pathbreaking in super metroid)
there's just something magical about that
"This is my accomplishment, and mine alone" (Obviously if someone else thought it up first, that's cool too, but it's still something that wasn't intended in the original game)