This is standard. Copyrights are assigned to the body that owns the project. For EMACS this is FSF, for AMP this is Google. The only time it's something different is if a project is owned by a foundation just for that project but super common in the OSS world. Have you done much OSS development?
One very important difference is that the FSF is a 501(c)(3) non-profit, and the terms of its charter and of the copyright assignment state that the software must remain free in the future. Effectively, the only thing the CLA does is make it easier for the FSF to enforce the GPL on behalf of the developers.
On the other hand, in AMP's case the CLA allows Google to start distributing the software under a proprietary license in the future, if they so desire.
I have done quite a bit of open source stuff and so far I gave manged to avoid projects which require a CLA. In my experience the projects with a CLA are a minority.
In many countries authors aren't allowed to put the code under the public domain. To avoid these issues it is instead preferred to provide an explicit copyright license.
AMP's license is technically Apache 2.0, but functionally, AMP's license is irrelevant. The only AMP code that matters is the code implemented on Google's servers for serving search results, as that is what everyone must comply with to be placed well on Google. Nothing about openness or transparency or governance of the project actually matters, because the issue is how AMP is used by Google on Google servers.
