You can change the look of so many of them, (maybe all, but I haven't tried all of them) that your observations/opinions, are only based on the default install.
I would object to the word must in your post however. I am not into Gnome/Cinnamon/Mate and use LXDE, because it is lightweight, but I adapted it to my preferences.
There was even a Linux distro (Pearos), that looked more Mac like, and I downloaded to play with, the week that the creator shut it down, after having a friend discuss getting a Mac (wondered what it would be like). I've heard talk that others are trying to bring it back/recreate it.