Should web browsers include popular web framework libraries?

Question

What reasons are there for web browsers to not have a library of popular web frameworks.

For example if a web page included jQuery, why shouldn't the browser have it's own static version, which is separate from the normal cached items?

I would imagine if most libraries were preloaded into a browsers cache, before any request was made with a document that included a library, then this would remove the initial request to a CDN and have a potential performance improvement.

But if the browser 'preloaded cache' didn't include the library then the browser should request the resource that is included in the document.