The same reason you might care about the artist or producer of a song: its context generally implies certain characteristics you might associate and appreciate.

For example, most Rust projects use clap which provides really nice command line help menus and also have relatively good performance in general.

> Why would you care what it's written in at all

Well, actually, it was the OP who said, literally, that "the most interesting thing about Fish (...) will be that it is now written in Rust"

In a sense why should anyone care about this article? It's a shell, why is rewriting it in Rust noteworthy?