I'm not sure I see any reason to expect or believe that engineers would make good ui/ux decisions. It's not clear to me that choices that are simple for engineering are necessarily even aligned with ultimately being functional.
A good ui/ux specialist will be interested in reducing error rates and improving ease of discovery and use through affordances and good organization of information and actions. Obviously other business interest may conflict with those goals but those same interests are capable of corrupting engineering as well.
And I don't think ui/ux work is as recent as this is all making it sound. Perhaps it is more common now even for orgs where their bread and butter isn't software but ultimately making tools useful and safe and accessible predates software entirely.