C# is the largest language for sure but it was designed for multiple languages from the start. There are things you can do in CIL and other languages that you can't do in C# even. Functional languages and pattern matching can be expressed quite well in .NET which aren't in C# (at least not yet fully).

I think the statement that the CLR ties you to C# is not justified. Can you elaborate why you think this is the case?

Also, WASM is not tied to JavaScript. You can't even compile JavaScript to WASM because it doesn't support the necessary primitives. In fact other languages that are completely different than JavaScript compile to WASM much easier.