WASM enables things like running a 20 year old CAD engine written in C++ in the browser. It isn’t a scripting language, it’s a way to get high-performing native code into web apps with a sensible bridge to the JS engine. It gets us closer to the web as the universal platform.
The biggest problem solved by WASM is runtime portability. For security reasons many users and organizations will not download or install untrusted binaries. WASM provides a safer alternative in an often temporary way. The universal nature is an unintended byproduct of a naive sandbox, though still wonderful.