I use the desktop environment I use for reasons that predate macOS/Mac OS X and are largely divorced from Microsoft Windows. I used to use the standard UNIX desktop environment, but then when I switched to Linux (since most UNIX software is closed) I had to find something similar. I tried fvwm/fvwm2+themes at first then found XFCE3 which had really similar goals to the standard UNIX desktop environment at the time. So I stuck with it as it became XFCE4.
So, there is an explanation about why Linux desktop users use different desktop environments that is completely unaccounted for by your macOS/Windows-centric theory. It also helps explain why there might always be more than one option.
Also, for what it's worth, the Common Desktop Environment was never that popular with Linux users but did become open source relatively recently.
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I use the desktop environment I use for reasons that predate macOS/Mac OS X and are largely divorced from Microsoft Windows. I used to use the standard UNIX desktop environment, but then when I switched to Linux (since most UNIX software is closed) I had to find something similar. I tried fvwm/fvwm2+themes at first then found XFCE3 which had really similar goals to the standard UNIX desktop environment at the time. So I stuck with it as it became XFCE4.
So, there is an explanation about why Linux desktop users use different desktop environments that is completely unaccounted for by your macOS/Windows-centric theory. It also helps explain why there might always be more than one option.
Also, for what it's worth, the Common Desktop Environment was never that popular with Linux users but did become open source relatively recently.