The other big benefit of popular frameworks to businesses is that they're more likely to reach maturity faster with more people using, fixing, and contributing to them. With frameworks, bugs, security holes, and performance issues - especially the hard-to-find edge cases and gremlins - once solved are solved forever (more or less), whereas every time you start your own new framework you have to deal with that again.

It's probably best for a business, if you want to give your employees experience architecting a framework instead of just using one, to standardize on something like Angular.js/Ember/React/etc and then encourage/incentivize your employees to become contributors to it. Almost best of both worlds - benefit from using the framework, and employees get valuable experience, resume builders, and connections. Only thing they miss in that scenario is architecting a framework from scratch, which is something only your early employees would have gotten to do anyway.