CSS only truly exists in a browser. As soon as we start writing CSS outside of the browser, we rely on guesses and memorization and an intimate understanding of the rules. A text editor will never be able to provide as much information as a browser can.
CSS is frustrating because you have to actually think of a website like a website and not an app. That mental model is what everyone finds so viscerally upsetting. And so engineers do what feels best to them; they try to make websites work like apps, like desktop software designed in the early naughts. Something that can be controlled.
The headline begs the question, but Robin makes this very insightful observation in the article itself: