If more powerful browser components would be available then designers would be happy to just style those, and functionality and accessibility would still be fine.
[1] graphic design is a completely legitimate field and a good way to get into UI design, but if that's all you've got, you still have quite a way to go
Take a look at the search page.
I don't believe there are many designers who are interested in creating experiences with poor usability, thus my point about ignorance and not understanding the tradeoff they are making. On "incompetence", if a designer understands fully that they are creating something that will be less useable and accessible for the sake of aesthetics they have earned the label. To take the HN search page as an example, the filters can't be interacted with via keybord or screen reader. When it's your job to help users solve problems and you have made it knowingly harder to do that, I don't see how that's competent.
Luckily, it has been my experience that in most cases(including my own) the former, rather than the latter, is at play.
It's true, and it really shouldn't be as controversial an opinion as it apparently is.