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.
This is very true. I once went to work at a .NET company which had built their own ORM and web UI binding framework. It was very nice back in the .NET 1.1 days but ASP.NET MVC, Entity Framework, the .NET base class library and the javascript community gradually overtook us. After a while it became more of a liability than a benefit. We'd never really documented it very well. New people ended up duplicating features and some of the quirkier bugs just never got fixed. Recruiting and retaining staff got hard and we ended up in a local minimum where each new screen was quicker to do in the in-house framework, but overall we were always falling behind.
It helped us to begin with, but my view is you have to factor in what the abandonment cost might be when the industry standard starts pulling ahead of you, and that could be big. As soon as it looks like the industry is settling on a standard way of doing something, start skating to where that puck will be.
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.