> Completely guessing, but the thought comes to mind that Rust was (still is? I don't keep up these days) portrayed as The C Killer. So to specify "written in Rust" was to imply "I wrote something low-level without C/C++" or "I rewrote Popular C Tool in Rust" in the name of memory safety.

As the OP, this is a big part of it. Rust might be a great language, but people announcing they rewrote grep (for example) in rust doesn't mean they've done anything special. The rust language team did something special. The person making the announcement just took somebody else's idea and reimplemented it for very little reason.

Great! You learnt enough to reinvent the wheel. Now do something useful.