In answering this, I'd look beyond just the language features and look at the background of how it caught on. What apps were built first. When did the "Rewrite it in rust" mantra take hold. What impact did but with colors / nice cli / sensible defaults have on things (e.g. fd / exa / lsd / bat / ...)? What libraries being available made it easy (clap / argh)?

Then look at how the community was built (e.g. Mozilla / conferences / forums etc.)

I've only recently started writing rust (after years of C#, Java, JavaScript, Ruby, Python, and a variety of other languages), and once I got past the basics of understanding borrow checker issues I love it as a language. Personally (for reasons unknown) I prefer brackets over indentation based languages, so Nim is a pretty hard sell there.

I don't know about all your other questions, and I realize your post was more about "why Rust?" rather than "why not Nim?", but that said the https://github.com/c-blake/cligen Nim CLI framework seems much lower effort / ceremony than even Rust's `argh` and is just about as old as `clap` (both cligen & clap started 8 years ago in 2015 - Rust argh is much newer).

There are over 50 CLI utilities in Nim at https://github.com/c-blake/bu, many of which do something novel rather than just "re-doing ls/find/cat with a twist". While they are really more "ls/ps construction toolkits" with some default configs to get people going, I think https://github.com/c-blake/lc and https://github.com/c-blake/procs are nicer than Rust alternatives. I mention these since you seem interested in such tools.