Why doesn't more add official support for Google Pixel 2 and 2XL?

Nexuses used to be the first phones supported by third party ROMs, but why not Pixels?

I think it’s because of the different mechanism of their update. the Seamless (A/B) System Updates

That’s highly possible… But I though this seamless update method was a part of the AOSP😂
I know nothing about Android Development though

i thought pixels have the most “original” android system installed, why still go for 3rd party rom which tried to be “original”?

Maybe this is just a part of Pixels. Of course I’m just guessing.
It seems that most other phones have only one system partition, but pixel is two,If the Pixels current system is A, then system updates are updated to B, and start to B, conversely, B updates are updated to A start to A.