It's not for me, but:

- Google is an American company

- GrapheneOS Pixel support depends on Google's Pixel support (and has been affected by Google's decision to open-source less of their Pixel trees)

- This OS promises to maintain the usable app store + cloud experience

- OS maintenance isn't dependent on a bunch of volunteers/donations

- You can just buy this from an official reseller rather than making your own or having a sketchy website pre-install a custom ROM for you.

I think GrapheneOS has the better developers when it comes to privacy and security, but there are reasons to go for the reliability of a corporate entity you pay for support over hacking together an alternative.