Why would you assume people are talking about themselves just because it's on HN? I'm reading these comments much more broadly.
I didn't mean to assume anything about the whole world, but we are talking about ourselves here, so our situations matter to us. I read the article as a thought experiment that is available to me personally and many others, even if it isn't practical for literally every human being.
And I don't think most people can't afford to save $400 a month. Lots of people save that much.
[0]: https://dqydj.com/etf-return-calculator/