The fact that the very developers of Angular have stated that Angular 2.0 will not be backward-compatible with Angular 1.0, and the reason why Angular 2.0 is be

The fact that the very developers of Angular have stated that Angular 2.0 will not be backward-compatible with Angular 1.0, and the reason why Angular 2.0 is being made is because the operating assumptions of browser capabilities when Ng 1 was made have changed radically.