Because sometimes people actually do feel that way. Sometimes it feels like your life is caving in on you. Sometimes people really do feel like they don't want, to exist, like they just want to curl up into a ball and go into that place between life and death. Saying "I don't want to exist" isn't saying " I want to die" it's saying " I wish that for the time being I could go somewhere and not have to feel". I don't think that there is anything wrong with that. And if you don't know how it feels to feel this way then you have no place to judge anyone that does.