It's looking light on the details to me. "It would be a lot of work to support other devices" is basically the entirety of it, I'm seeing no detailed hardware requirements for a phone to be a candidate except "made by google."

Understand, I'm not attacking anyone here. I will be buying a pixel and running grapheneos on it very soon. But I still wonder, when you say "only pixel satisfied these requirements" why, particularly, is that the case?