It may be permanent and I think this was the official indirect response:
"AOSP needs a reference target that is flexible, configurable, and affordable — independent of any particular hardware, including those from Google." [0]
Emphasis on independent of any particular hardware.
Current speculation/inference suggests it is because of the antitrust case against them, preparing for the possibility that they may be divested of Android (or at least to decouple in meaningful ways [1]).