Many people—though presumably not you, because you saw this disease-riddled book and said, “That is a book for me!”—don’t like hearing about the more gruesome aspects of life. In general people want to read about happy stuff and to feel good and to look at puppies wearing party hats.
I think I've figured it out. She's trying to write like Jenny Lawson (Let's Pretend This Never Happened, Furiously Happy). Except this isn't a humorous book about her struggles with depression and it doesn't make me laugh out loud. And she's talking about puppies in party hats and not taxidermied raccoons (just go read Furiously Happy).