Privacy

The moment the cops get physical access to the device it should be considered compromised, regardless of you have Graphene, Bismuth, Borophene or whatever. Since if they (the cops) are any well-equipped, they'll just disassemble the phone and proceed to make a copy of the raw memory as-is, then take all the time they have in the world to work on breaking through the copy rather than directly on the phone (and risk eg.: a duress key activation). Rinse, wench, repeat.

(I do get that Lineage requires having a bootloader unlocked which is usually non-relockable. But that's just the breaks. Neither Graphene nor relockable phones are common enough to account for the amount of people who would or might have to protest)