1. Developers with a wide range of understanding of UI from negligible to acceptable.
2. UI experts who actually understand code.
3. UI "experts" in industry whose only skills are image editors.
4. Academics who did said research.
Seems like the entire problem is the ascendancy of Camp 3 which decision makers who being ignorant of technical matters themselves can't tell from camp 2.
That's my impression too. Camp 2 is also a problem when they decide to improve things under heavy time constraints, but it's mostly camp 3 being the issue, and camp 4 being ignored.
Meanwhile, camp 1 mostly won't break anything by themselves (developers do usually learn enough UX for that), but also are unable to fix anything.
I'll just add that camp 4 didn't exist only in universities by the time those things got developed. But they almost only exist there now.
Those conventions were created by usability experts after years of research. It wasn't simply programmers building them back then.