But to be fair, Nix is not the only answer to that. There are lots of tools for just dotfiles but you can also build something using e.g. ansible to manage everything.
All my computers have their config in a git repo. That includes users, packages, services, dotfiles, /etc configs and so on. I used ansible before writing my own tool. I can install Arch from scratch and only need to partition, run one script and then apply my config on first boot using my tool to have my system restored. I know it's not as declarative and absolute/reproducible as Nix, but it works and it's way less painful than my last attempt at giving NixOS a go.
I do it, too. I rarely read any text without subconsciously marking the text while reading it. Might be a tool for me (ADHD) to make it easier not to lose track - I don't know.
But regardless of why people do it and while I agree that it's probably something very specific not a lot of users do, I refuse to believe that anyone actually uses those select->popup-> share features, ever. Often the little pop-up even blocks the text above it which is just insanely bad UX imo.
Sites should never mess with core functionality without asking (scrolling, selection, tab/keyboard navigation, hijacking common shortcuts/right click, clipboard, history, etc).
I believe someone came up with that idea a decade+ ago and people just want it on their site to add value without actually checking if anyone uses it.