Well, because as others have pointed out, languages like that have existed for at least a couple decades. Most of the 'nice parts' of Rust are really borrowings

Well, because as others have pointed out, languages like that have existed for at least a couple decades. Most of the 'nice parts' of Rust are really borrowings from the ML family of languages: Hindley-Milner type inference, algebraic data types, and pattern matching. OCaml or StandardML, (or Haskell if you want to get funky ... I don't), F#, Scala, etc. Hell, these days even Swift, or Kotlin, have these features. Which I'd call: modern static type systems. And I understand even Java is getting some of them. Even TypeScript is a reasonable-ish solution with a pretty nifty type system, if you don't mind the (non-existent) threading model. I like Rust, but its niche is: the above nice things and a clean syntax, but without the latency&pause costs of GC. And that's what I use it for, when I need that kind of thing, for systems programming. And for that, the killer feature is the borrow checker which makes using the above features relatively painless, despite having no GC. (Now one other advantage of the borrow checker is its application to concurrency -- making ownership of locks, and mutable state generally, easier to reason about. That's perhaps a killer feature that the other languages I mentioned don't really have)