lol, tons of reasons... a few off the top of my head; routes are central to EmberJS and are key to SPAs. AngularJS uses primitives as models which means that at the kind of scale we are hitting in our apps performance suffers (dirty checking 10k rows is killer) (also, computed props are easy, and we're into UAP). EmberJS' caching rocks.

But the big one is -- Google. When are they gonna pull the plug on AngulerJS, how broad is the contribution base outside of Google, and not using YUI was already a battle...