> I have never understood why people felt the need for all this desktop customization and setup.
Compatibility with existing muscle memory.
In 1989, I took a .twmrc file from a friend, which mapped alt-mouse1 to move, alt-mouse2 to resize and alt-mouse3 to iconify. Those mappings became muscle memory over the next 17 years of twm and ctwm and KDE use.
At that point, my whitebox died and I decided to get an iMac because I was very busy with work and personal life, and didn't want to spend a lot of time building/configuring a new whitebox. MacOS was *nix, so how bad could it be? Well, I ended up fighting MacOS tooth and nail, as I could never get my mappings to work reliably. That lead me to use X11 for a lot of things, but that inter-operated poorly with native apps. After about 9 months, I gave up on Mac as a desktop and gave the iMac to my then-inlaws and built a whitebox.
So I feel strongly that the ability to tweak things like this, even if they are never used, can be crucial to some people.
In fact, I'd very much like to covert to using my M1 mbp as a desktop with a dock, but I simply cannot function using Mac's window management on a deskop. I've tried all kinds of tweaks and add-on to get the behavior I want, and they all fail in some way.