The amount of diversity in JavaScript frameworks is NOT good in my opinion (a back end dev who needs to get a bit of front end stuff done every so often).
It's not like you have to use all or any of them. It's more of a problem if you're a front-end dev looking for work and feel obliged to learn whatever is trending at the moment.
Really? You have React, Angular and Ember. Three libraries or frameworks for building web applications. If you aren't building a web application you might not need any of them.
Just use React as the other two are copying/converging toward React.
All the other web app UI frameworks? Noise, they won't amount to much and add very little. The last release worth paying attention to was React 2 years ago. Hardly a breakneck pace.
Angular 1 or Angular 2? What about Backbone? Meteor? There are a LOT more than 3 frameworks. The choice is overwhelming when you are not a specialist in JS and its difficult to know where to begin.
(Though having tested React recently, its the best of the ones I have used).