It’s more complex than that, as there’s tons of academic work essentially proving it’s impossible to chain two independent garbage collectors and not end up with stuck uncollectable memory (I apologize, this isn’t my field, I’ve skimmed the work but not retained the citations, and I realize how counter-intuitive that result is... nobody wants to think its true, so it keeps getting more academics thrown at it, without changing the results).
My assumption is that at the moment they are just accepting that some uncollectable memory will happen in the short term and eventually the WebAssembly working group will expose the underlying garbage collector and everything will get better. Early days kind of issue for now.
In the WASM case it's trivial to show how this is the case at the moment: WASM just has a large ArrayBuffer, which the JS GC will hold on to all of, regardless of how much the GC in WASM deallocates.
My assumption is that at the moment they are just accepting that some uncollectable memory will happen in the short term and eventually the WebAssembly working group will expose the underlying garbage collector and everything will get better. Early days kind of issue for now.