C# - gives you similar syntax with a better ecosystem + tools. if it's just types you love Java, Kotlin, Golang the same. Better languages better tools, better ecosystems.
typescript on the backend shows people have more money than sense.
maybe after all i'm lost on the incentives.
It's just a no-brainer when it's a good fit and you already have competent devs. Then there are advantages like being able to share types across your entire system without having to resort to code generation.
On top of all that, we have Effect which is easily the best and most robust way to write production grade typescript. It's nearly a language into its own and sort of should be, but we are fortunate that we can instead have and use such a useful tool in the most popular ecosystem in the world.
Plus many SaaS vendors now have node only SDKs, so if I want to use C# or Java, I have to advocate for the team to write their own REST bindings, instead of using the existing SDK, naturally a quixotic battle that I won't bother with.
In favour of Typescript, it has been designed by the same key architect as C#, so I don't feel that bad using yet another language from one of my language designer heros.
And if I need some additional perf on the server beyond V8, there are always native node modules.
2) JS is "trusted" in more places (or at least considered far more easily "sandboxable"). There are several large "serverless" or "cloud-native" hosts that will let you run all the JS you want at large scale, but have far more hoops to deploy/run other languages, and sometimes if they do support it they support only when compiled to WASM.
Code written in those languages tend to embrace nineties-style OOP with classes and inheritance. node.js is generally functional.
All the front end Devs know Typescript but may not know any other languages aside from JavaScript/html/CSS