Desktops are extremely personal things. What works brilliantly for one can fall dead flat for another.
Cinnamon is nice if Win9x UI conventions are what you’re comfortable with. That’s not the case for many Mac users, especially those who've been using the platform for upwards of a decade, and unfortunately there is no macOS analogue DE for Linux. So even if some of these users might be interested in switching, they’re staring down learning a whole different set of conventions and key shortcuts, fighting muscle memory for several weeks, and still not being as fluid in day-to-day usage for several months at minimum, which seems like a pretty awful value proposition when they can pay $5 to fix a minor quibble and continue on with their day.
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No desktop environment is capable of full Mac-like operation. None have an application-based paradigm for example and instead all use a Windows-like window-based one instead. While it’s possible to get a global menubar on a couple, the feature is hacky at best and only works properly with a handful of apps.
Rigidity is only a problem when the broad strokes aren’t congruent with the user’s desires. This is why a lot of longtime Windows and Linux users have trouble with macOS while longtime Mac users install a couple of third party utilities and are perfectly cozy.
macOS ergonomics aren’t perfect, as they aren’t with any OS, but are perfectly functional if you know your way around. Navigation is not a problem if you’re using key shortcuts for both switching apps and windows for example and don’t have a solely window-based mental model. It’s been possible to maximize windows without fullscreen by holding down option when using the key shortcut or clicking the green button.
Permissions are a growing pain that every desktop OS will eventually need to face. The old model of every app having access to everything whenever it wishes doesn’t work in the modern era, and dealing with that is something seen even under Linux with things like Flatpak.