Generally, those people are experienced users that know exactly what they want out of a distro and don’t really need help for anything. Those distros usually do a few things that the user is seeking.
For example, for some people, typing their thesis in LaTeX using emacs is the better workflow. To any average person that sounds insane when Microsoft Word is so easy to use and does the job just fine. But they enjoy it, it works for them, paper gets written, everyone is happy.
Distributions are a spectrum between novice users and expert users. Some people want to put the USB in and be good to go. Some people want a very precise setup for very specific needs.
You may ask, why not start with Ubuntu/Mint/Pop and remove what you don’t like? Well, it’s much easier to start with a blank slate than making one by chopping everything out. For my particular use case, I moved to Arch in big part because I got tired of the mainstream distros getting in my way, and wanted to start the other way around and only install and configure what I want, the way I want it. So Arch for me.
I know experienced users that really don’t care about messing around and are happy with how it runs out of the box and are happy with the development environment provided by something like Ubuntu/Fedora.
And then there’s my box which is a NAS, a workstation, a media PC for the TV, a build server, and a few other things, and it’s all dynamically reassignable. Friend can pick up the controller in the TV room and a GPU gets assigned to it and starts up Steam in Deck mode on the TV, while I can still do my stuff and game on the workstation side for local multiplayer. If the game needs a server, no worries, it’s a kube node, I can temporarily transfer the server locally and back on one of my real servers. Guest needs a PC? Sure, take this monitor and this keyboard, here’s an ephemeral Windows install. Sure, I could probably twist Ubuntu into doing all that, but it’s one hell of a lot easier starting from scratch.