Guest languages introduce additional layers to debug, usually lack in tooling vs platform languages, require additional FFI considerations, their communities tend to create their own libraries and build tools to parallel platform libraries and tools, just to be more idiomatic.
Also they aren't guaranteed to be around forever.
Platform languages stay around while the platform is still relevant.
So, Kotlin is Android's Swift. Outside Android I bet that in 5 years it will be as relevant as Scala and clojure are today.
TypeScript is a wonderful language from Anders, but tsconfig.json allows to change the semantics in multiple ways and it is relatively hard to track down what changed in every release.
F# is only partially supported across all .NET deployment scenarios and VS Tooling. It was even left out of the new WinUI roadmap announced at BUILD 2019, even though .NET Core does support it.
