This website doesn't even set a font size. The font size is just your browser's default. You have your font size set too small. This website is one of the few examples of doing it right. How can a web developer know what your requirements are? Only you can know that. There are many bad things about the modern web but fortunately being able to set your own font size is still a thing.

Firefox even lets you set a minimum font size. And there is an option to stop websites overriding your choices which helps with sites like HN (but not the one you are complaining about) which explicitly set a small font size.