Take Rust in Linux, for example. Even with support from Linux’s creator, Linus Torvalds, Rust is moving into Linux at a snail’s pace.

Because Linux is the biggest software in the entire world and they do lot of stuff their own way. Rust is integrated slowly for future new projects. It makes sense to move in snail pace. The government doesn’t suggest the Linux project to stop using C entirely. The government “recommends” to start new projects in memory safe languages, if it is a critical software. That makes sense to me.

Doubly so... Don't care what the language is, or what the advantages are... Even if there's a considerable security advantage to a new language... There's no such thing as a language that's advantages outweigh the security risks of rushed development to convert decades of tested code.