It also has very frequent updates, and my phone will get them for a long time (also true for the Stock Android on Pixels, but that one really sucks), which was also very important for me, as I want to be able to use my phone as long as possible.
What made this even more appeling is the possibility to install sandboxed google play in a seperate profile/user for apps that really need it, which works surprisingly well, and even then the google play services don't run with elevated permissions like they normally do, but with the same permissions like other apps.
And the battery life is insane, if I don't use my phone it basically does not loose any battery, and even with heavy usage I don't need to charge it daily.
So GrapheneOS was the easiest way to start degoogling (kind of ironic using Google Hardware) my mobile phone, while still being able to run nearly all of the Apps I need.
Many of those are appealing