I suppose that for the platform provider it's easier to ship only one runtime and then run everything over it, also might be better in terms of security because

I suppose that for the platform provider it's easier to ship only one runtime and then run everything over it, also might be better in terms of security because of the sandboxed nature of WASM. Once WASI gets stabilized, you will also have the option to mix JS with the other languages that already target WASM, so your infra could be build on top of different languages and change them according to the requirements, just think of you build your entire system in JS, compile in modules and deploy them as components, then you can swap one component at the time when necessary.