> It would be neat if those services could be written in Swift, so that I could just use the language I already know

Then somebody else would have to now learn Swift even thought they write in different language like: Android Developers (Kotlin/Java), React Native devs (JS/TS ), Windows Devs, Linux Devs etc. As long as Apple don't invest more in official cross-platform tooling Swift is not gonna be mainstream (even though I like Swift). They have to bless other competing platforms.