I looked in the GitHub issues and there's a closed issue for F-droid inclusion. The author states that F-droid "Doesn't meet their requirements" but doesn't elaborate. I wonder what F-droid is missing that they need so much?
I understand that the author trusts itself more than F-Droid, but as a user the opposite seems more relevant.
I'm not really sold on the argument... Also constant push/hype of GrapheneOS (and the "attitude" of it's devs) is mildly annoying...