Very true. I made a point of doing it by forking an already working nix-config from github that used what I wanted to use. This one drew me in because it used xmonad along with home-manager and flakes. Honestly, it really WAS pretty confusing at first (due to that setup using secrets and git-crypt to obfuscate some of the files) but Nix had some helpful error messages that allowed me to finally get it working in a VM. Then, I got it installed as my daily driver when it was stable enough. Today, I provision all of my different systems in my network (ARM, x86, Nix-Darwin, Nix on a routers and network gear, etc) using one nix-config that contains all of the machine configs as different outputs.

I'd say that the upfront costs of administration are too high for most people's use cases too. It's the same reason why most people don't document most of what they do, most of the time it's the right decision and it's hard to tell what the exceptions are until after you forget what would be in that documentation.