The obvious answer is people who grew up using Macs tend to like the Ui and workflow.
Even though I've never enjoyed my times using MacOS, I'll still sell being able to perfectly clone it's desktop as a feature of Linux for those who do.
I wouldn't use a complete macos theme with the logo and everything, but the mac design language does have some pretty nice details that even help usability.
For example, I love the double outline that macos windows have, the normal darker line and another lighter inside. To me, it really separates windows when I am working with several, and they overlap (I use mac at work), in addition to looking nice and giving some depth. That's just a little detail, but there are many like that one that is easy to see why someone could appreciate them.
Obviously it varies from person to person, there's also stuff that I don't like, but I do can see why someone would use a theme like that.
It kinda makes sense to me; my KDE desktop is basically set up like Windows in terms of layout (not theming). It's what I'm used to and prefer the familiarity.
I can imagine people who are used to MacOS like the familiarity of GUI layout and the aesthetics too. Also in fairness to Apple, it is an aesthetically pleasing desktop even if the layout and GUI elements (such as the dock or the top menu bar) isn't what I like.
MacOS is very user friendly (in my use-case. Everyone has different needs). I like they layout of the top bar, the dock front and center, the fullscreen "launchpad" as opposed to a start menu, etc. To each their own.