Thesis: most desktop GUIs are not opinionated about how you interact with things, and this is why there are so many GUI toolkits and they make so little difference to programs, and also why the browser is a perfectly good cross-platform GUI (and why cross-platform GUIs in general).
Some GUIs are quite opinionated (eg Plan 9's Acme) but most are basically the same. Which isn't necessarily a bad thing but it creates a sameness.
(Custom GUIs are good for frequent users, bad for occasional ones.)