I think they know that they are unwell and going to die soon but they just ...don’t care. I think their life has always been so boring, pointless, and self-absorbed that developing a host of chronic diseases is an entertainment in itself. Once you are so engulfed by fat it’s a point of no return. Your body and your life options in general become severely limited; once the realization hits, eating  themselves to disability and early death becomes a reasonable option.