"UI design is certainly a different discipline; it may be a slog for you but it's bread and butter for those who like doing it. "
And I just wish they'd stop doing it an leave well alone.
Back in about the 1980s we had the CUI guidelines which a lot of early GUI S/W more ore less followed (I know Liam has complaints about the less aspects) but it resulted in a fairly standard design language. Then the UI and UX designers got busy. On the one hand it might have simply been gratuitous busy-work for idle hands.
On the other, I strongly suspect Microsoft threw its weight about to impose the ribbon interface on its victims so that after a few years new users wouldn't understand the FOSS competition's UI which continued to follow the same lines as older versions of Microsoft applications. I also suspect them of having made top-posting the norm for similar reasons whereas we oldies always saw it as an indication of newcomers who lacked the wit or manners to see and adopt netiquette norms.
In consequence what was regarded as good practice and still followed by some FOSS developers (Mozilla fell from grace a long time ago) is seen as "difficult" or "hair-shirt".
There are also instances where FOSS just does its thing for very good functional reasons. The vi editor is one, of course and regular users would not swap it for an editor hampered by a "conventional" but less functional UI. Another instance is the Gimp save functionality discussed about. Pinta is more conventional and all too easy to make the sort of mistakes avoided by having a choice between "Overwirte", "Export" and "Export as" options as well as "Save" depending on the use case.