I don't think it's necessarily because of lack of generalizability. We (SWEs) built it, so we naturally have the most intimate knowledge of how to dogfood/use it. And so the cycle intensifies (use, provide feedback, improve). There's many positive examples of LLMs being useful in document based workflows in other domains as well!
I relate to your comments about gym a lot. I feel like going to the gym is a mundane, mechanical and very dystopian activity. I never found any 'fun' in the gym and we all know we can't force ourselves doing what we don't enjoy. So I set out searching for physical activity (hopefully strength training) that was fun.
After a lot of trials, I found the answer: F45. Their workouts are pre-designed, group based and <45min. Working out in a group brings evokes some primitive, deep sense of camaraderie that I find very rewarding and motivating. The fact that they are <45 minutes including warmup, working out and stretching makes them really quick for me. The stations are all setup before so I don't need to expend mental or physical energy in setting anything up. And the exercises are super well-designed, so I can leave my brain at home knowing full well that I'm going to get the best results. As an added benefit, my local f45 has a great trainer that helped me heal from injuries and always looks out for my form, so I can focus solely on having fun.
It's honestly been a game changer. I vividly remember moments where I was having such intense sense of euphoria despite being in so much pain. I whole heartedly recommend anyone to try group based HIIT workouts.