The problem here is all the OS features are discarded. Can't insert password from password manager because to do so the page would need to access to passwords. Can't use the user dictionary because to do so would be a privacy issue. Doesn't support CJK and other languages that require an input method editor. etc....

It also means a platform's features are not duplicated so your app's behavior sticks out as having a different experience from everything else the user does making it frustrating.

That said, if you want see an app in WebGL/WASM where the browser is rendering everything there's https://earth.google.com as a high end example. It has most of the issues just mentioned as well as the fact that nothing is selectable by default. Want to copy a name so you can paste it into your search engine of choice. NO! Want to right click on a foreign name to find out how to pronounce it? NO! etc....