> there are hugely successful open source projects, but they are generally components of larger proprietary products

Not "but", but "so": "... so they are generally components of larger proprietary products".

No you aren't. MacOS' interface is not ugly by itself; but it is awful in a sense that EVERYBODY tries to mimic it. As a result of that, we have a great choice of quite similar, cargocult-inspired GUIs.