They couldn't answer the question most on my mind: "We’ve reached out to Google to inquire about why a custom ROM created by volunteers is more resistant to industrial phone hacking than the official Pixel OS. We’ll update this article if Google has anything to say."
GrapheneOS makes security trade-off that are inconvenient to the user. This results in a far more secure device, but nonetheless a device that the general public would find far more annoying. Google would lose a proportion of its user base by implementing the same protections.
Example: https://old.reddit.com/r/GooglePixel/comments/ytk1ng/graphen...
Also Google Pay is missing.
Which particular thing you consider inconvenient or even annoying? You can even install Google Play there.
I see just one minor tradeoff - no face unlock.
Google OS-level integration is absent, and while Google Play Services can be installed, you're still missing things like Chromecast. Also, there's more manual configuration (although I don't remember exactly what, I've never used GrapheneOS). A lot of stuff you do get for free, but not all of it, and stuff that's been removed as a "feature" isn't always stuff that nobody wants.