Their support of Pixels with AOSP has been well documented! This has always been one of their selling points, as a sort of reference device. I've exclusively bought Pixel phones in recent years and this is one of the primary reasons.
Of course Google never made any guarantees, and a rug pull was always possible, but it's absolutely still disappointing and well worth commenting upon.
Just the name change is telling. "Pixel" suggest a focus on pictures, whereas "Nexus" suggests a focus on Android itself (inspired by Nexus-6 androids in Blade Runner).
AOSP recipes themselves list reference devices and they could have updated this with their announcement in March if they didn't want external developers procuring these things as bricks for their gardens. GrapheneOS is just a community of a AOSP derivative there are any number of AOSP derived things people may have been doing with these devices.
Or, how about Hackintosh (from yesteryear). Apple gave 0 support for it all those years when folks made it work, and one day it went away - and I dont remember saying Apple, please support Hackintosh.
They made related announcements in March and certainly saw interpretations of their announcement by interested AOSP derivative maintainers.
That's not remotely the same as I figured how to boot X against so and so's wishes and now it stopped working.