From the comments:
Part of what we’re trying to do is get the benefits of AMP without publishers having to “give away all of the control” of their content by putting it under Google’s domain. AMP, if it only works on Google’s infrastructure, poses a challenge to an open Internet. If we can help ensure that it’s truly an open standard then it can help cleanup a lot of the mess that is the current state of the mobile web. We have a lot more to come on this front. Stay tuned.
I get the need, and I think it’s a noble effort but I still feel like AMP is slowly breaking the link-ability of the web, URL by URL. So we now have 2 silos instead of one, great, but we used to have many orders of magnitude more than that.