Idk, maybe what Arthur said? Though planes are pretty safe anyway, your chances of dying in a plane crash, at least in a commercial airliner, are pretty slim. But I think turbulence is a bigger problem for planes in the back than in the front, and turbulence is very inconvenient and at worst can break your bones. Also, seats further away from the engines have less noise. And also it could be a factor that seats closer to an escape hatch may be preferable to some people, unless it's right at the escape hatch, in which case people might prefer not being there because they'd have have the responsibility of opening it if there's a crash. (And yeah, crashes are again rare, but the stewardess has to take some time before the flight to teach you how to open it and stuff..)