[DaveStein]

I can actually code JS fine without a framework. However do I want to keep up to date with all the idiosyncrasies of a growing number of browsers? Do I want to rewrite every function that exists in a framework, such as getting the height of an element or the viewport? No.

The speedups in frameworks are realizations of better ways to do things that a group of programmers came up with - which is almost definitely going to be a better way of doing things outside of a community. That argument would only work if your functions were always as fast as possible at start. Don't forget Chrome was already the fastest browser out there for JS, and they still have improvements of 50%+ in updates.