I’m sure experience is part of it, but having worked with CSS since roughly 1996 I’ve noticed that there’s a heavy respect gradient where a lot of developers thought it’s beneath them, not a real language, etc. which is also shared with HTML, the layout model, etc.
None of that is universal, of course, and it’s not like CSS is perfect but the worst code I’ve seen was written in near-contempt by, for example, some dude who wrote many thousands of lines of … not brilliant … code to make a Java display framework because he refused to learn how CSS works. I was called in to that for performance reasons because if you don’t understand classes, you can end up with 20MB HTML responses with the same inline styles everywhere. That was an outlier but I’ve seen a lot of similar attitudes where someone shipped 4MB of JavaScript to avoid learning CSS positioning or tried to get a designer to edit their code because they thought adding IDs or making semantic, accessible markup was beneath them. One interesting social dynamic there has been the guys who simultaneously refused to deal with front end stuff but also didn’t think it should pay well, often with more that a whiff of sexism given how designer was coded female at those places.
That’s improved in some ways as front end work became more central in the SPA era but it’s still pretty easy to find people who’ll deploy enormous amounts of code to avoid using a builtin browser feature or whine about how “the DOM” is too slow as if it’s the browser’s fault they’re using React.