By level of investment, both me and the OP meant in terms of products that are key to the company's operations, and need to be continuously supported and improved. Facebook is one such app for Facebook that uses React. Instagram is one such app for Facebook that also uses React. I honestly don't know any such app for Google that uses Angular. Until that changes, there is very little incentive for the Angular team to keep improving upon the existing solution instead of building something completely new with no regard for the people that depend on it.

The so called upgrade path they offer for Angular 1.x is a complete joke. That you can "mix Angular 2 into your existing Angular 1 application" would be a true statement with any component-oriented framework in place of Angular 2, like React, and Ember. And this was not true for Ember just a few months ago, which is living proof that gradual improvement can in fact be accomplished with any framework, but of course, throwing everything away is much easier, so the framework developers need to have strong incentives to not do so.