I thought you meant adding other scripting languages to the browser. Not a WASM runtime. That's likely still not a good idea. A specific runtime is likely to b

I thought you meant adding other scripting languages to the browser. Not a WASM runtime. That's likely still not a good idea. A specific runtime is likely to be outdated fast. That's like asking why the JQuery library wasn't shipped with the browsers themselves. For runtime with a significant size, it's probably going the same way as JQuery. Have a CDN host it so different websites can use it and leverage the browser's cache.