Do you do any type of web development? You don't really have any choice if you do. You can do a lot of things server side, but once the code has left your server, your technology is limited to what the users browser supports.

All browsers I know of support JS(EMACScript), HTML, CSS. They may support other things, but often not all of them do. Javascript itself is a very basic language, and a lot of the build in methods are either not intuitive or are complex in its access and you have know the nuances of the language to work with it.

These frameworks often provide more intuitive access to JS by applying patterns such as MVC on top of JS. You could do this yourself in JS, but why?

I will give your question credit that it does seem like there are a TON of libraries for Javascript and it seems like every day there is a new library promising something in Javascript.

TL;DR: Javascript is the only widely-supported way of coding in a browser.