There was a reason for this. Google always branded pixel and nexus devices as a dev kit for Android OS. So all different brands of Android phones started their OS development with pixel. But last year Google announced they are no longer recommending pixel devices as the backbone of Android OS development and that companies and users should target cuttlefish their emulator for AOSP. With that they also stopped sharing device trees and vendor blobs. That is nothing new for custom ROM community but Google always provided that and that made custom ROM development really easy with very fast update cycles. I'm just hoping they don't lock down Bootloader like others