I'm sorry, I'll be honest: I always thought AngularJS was kind of weird. I never really understood why did people start liking it in the first place, so I'm not surprised people are migrating away from it.
Angular.io on the other hand does a lot of things right. There is also some beauty in it, most components are specified as CSS+HTML+JS, and it reads in that order from top to bottom in one file. That's kind of cool. But I don't have hands-on experience with that framework so I don't have any qualified opinion.
All that said, there is also a strong network effect when it comes to adopting technologies. People just use what most people are using, and that's because it's the easiest to justify: the most popular solution is the least surprising solution, and people can get defensive or scared of risks when it comes to new and surprising stuff, so they prefer to have a feeling of "safety" that comes from picking something familiar (I'm reading a psychology book about these effects). At the moment, that seems to be React.