WebAssembly is not without tradeoffs either. I'm not an expert, but it's often heavier due to bundling the native language's stdlib; it's annoying to interop with the browser environment because that's still JavaScript-tailored; it's also just hard to write code that can be compiled into WASM (e.g. in Rust, it needs to be `#[no_std]`)

If you're doing real work, you don't interact with the browser.

If you're just glueing things together between APIs, then JavaScript is fine, and static typing would just get in the way.