Js has evolved since the initial version, which also absorbed the knowledde from other existing languages.

But my main point is the years and years of excellent engeneering in js implementation. Languages compiling to js can utilize its gc as well as many optimizatoins js engines such as v8 provide.

For example, if your language allows to dinamically create key-val objects, the language could automatically benefit from hidden classes v8 creates. Implementing the same in wasm would be much more difficult.