This is the second most gotten achievement in the game, the first being "start the game" at 93.6%. That gives a 1.8% margin of player who either started the game and never died, or started the game and quit before dying. Given that the third most gotten achievement is "defeat the first boss" at only 68.1%, the sharp decline makes me think most people just quit.
It's also possible their game crashed. This IS dark souls 2 we're talking about.
It's also possible their game crashed. This IS dark souls 2 we're talking about.