Those are all fair points and people do write books or do stuff off their bucket list while being happily and gainfully employed.

But people are different and not all jobs are the same. Some people don't have the time or energy [1]. Add the stress of supporting a family, a demanding boss and the fear of losing healthcare along with your job and you'll get to your bucket list either during the scarce vacation days or in your late 50s early 60s (if you're lucky).

This is what FIRE's all about. It's about freedom basically. Money == freedom to do whatever you want to do without fear of losing the bottom of Maslow's pyramid. This is especially valuable in the US, where there is no social safety net.

[1]: https://en.wikipedia.org/wiki/Spoon_theory