It’s kind of the same argument as that for Node: having a singular language for everything you do lets you have “thick” tightly coupled packages that do everything, which you can compose or decompose in a safe(r) refactor as business needs change.

Once you start using JNI or Objective-C++ to hand off “computationally expensive” work to common C++ (now Rust) libraries, you end up needing to become an expert across a lot of areas.

If 95% of your competitive advantage lies in doing things everywhere with low memory, then taking on an additional 2-3 stacks (SwiftUI + React + Compose) as well as all the bindings and build system and etc overhead can be pretty gnarly.

If 95% of your value add is in your web-based UI, consolidating to a single JS stack of React + React Native + Node can greatly reduce your idea-to-market time, I’d imagine a full Rust stack could do the same if your value add requires maximum performance and only a little UI iteration.