At Oxide, we named the company after Rust, but we use TypeScript on the frontend, not Rust. Rust is our default technology choice for most new code, but TypeScript is for frontend code.
Rust on web frontends is just not super mature. You can do things with it, and it's very cool, but TypeScript is a very mature technology at this point, and gives a lot of similar benefits to Rust. And it can live natively in a browser context, without complex bindings.
I don't work on native macOS apps, but I'm assuming it's similar: Objective-C or Swift are expected, so you end up needing to bind to APIs that aren't always natural feeling. I could see why you'd want to do something similar: write your core in Rust, but make the UI stuff be in Swift, and call into it from there.
Could you please elaborate?