Why should I use this over JVM?

Almost any other language can now compile to WebAssembly: C/C++ via Emscripten, Rust (it's already bundled), Go and even Swift.

That offers a very nice transition to the WebAssembly ecosystem, so you don't need to rewrite your business logic in other language (in contraposition to the JVM)

Basically UNCOL, TEGRA, AS/400 TIMI, z/OS ILE, CLI, ...