Wasm doesn’t have any built in garbage collector (yet) and so by building on top of Javascript (especially for a language like Lua that has a lot of alignment w

Wasm doesn’t have any built in garbage collector (yet) and so by building on top of Javascript (especially for a language like Lua that has a lot of alignment with it) you are reusing that machinery which is easer. True you could take an existing lua implementation and compile to WASM but then as the other comment explained interacting with the DOM would need to be implemented.