What would that choice look like in practice? Should every browser vendor implement and maintain a dozen different language runtimes with all the associated compat and security implications? Standartising on a common scripting language seems like a pretty reasonable engineering decision, and abadoning that standard after decades of widespread adoption seems like a pretty shitty engineering decision.
> What would that choice look like in practice?
Allow WebAssembly to directly access the DOM, so you can write whatever language you want and compile it to WebAssembly.
This implies the massive complexity of restructuring how browser engines work, plus working around security and memory safety issues. And this work is actually being done right now, see wasm GC and Component Model