I think it's because it is hard to relate to the inability to achieve/regulate sleep, which is something that is as natural to most as breathing.
It's also hard to comprehend the full consequences of sleep deprivation, etc., with N being an "invisible illness" and all... especially with the social stigmas attached to most of the very limited treatment options.
Try to relate as they may, the best people without N can do is think with "Oh yeah, I'm tired too today... I didn't go to bed until 3am. I bet this is how it feels!..." and it's just like, NO. lol.
It's impossible to imagine the physical, emotional, spiritual, and psychological frailty N can make ya' feel unless you've been there... On the good days, I feel almost-normal. On the bad days, I feel like Lady MacBeth!