Uhm, the web is to share content, not to play JS
The web doesn’t have a single unified purpose. Even if I hate it as a programming language, JavaScript if the basis almost all client-side browser operations build upon.

Sure, a simple website which just contains information works without it, but if you design a website in which the client does anything interactively and not everything should be processed server-side, it’s not really possible. No matter if you’re talking about a web game, something like Google Earth or an in-browser editor.