But way more difficult and with a much higher attack surface area.

And also, it's not necessarily apples to apples. It would be nice to be able to drop a compiled WASM module into your codebase and use it from just about any language on the backend. You could reuse a lot of code that way across different services without the overhead of spinning up yet another container. And you could potentially even run untrusted code in a sandboxed way.