If it were just the bytecode then it would not have failed. JVM bytecode and WASM have plenty of similarities. What cost Java is the stdlib surface area and security model. Also that it is a separate runtime was annoying, like Adobe with Flash, there was one primary vendor.

So many JVM bugs and a huge stdlib. WASM has no real lib, and when it does, it's security model is already restrictive... there's no disk, network, threads (yet), etc.