They need to meet the security requirements on here:

https://grapheneos.org/faq#future-devices

If they don't then we aren't interested in supporting it. Users will just paint flaws caused by less secure devices to be a GrapheneOS problem.

Some are just totally incompetent, for example, Fairphone 4 set ther verified boot keys as publicly available test keys, meaning anyone can just sign an update with those same keys. Samsung kills certain device features via an eFuse when the non-stock OS is installed. 

 Great now i understand what are trying to do.
Thanks