While that is true yes, their whole brand is built on being secure.
but if calyx would take their features they would be screaming loudly how unfair that is
If they release to Fairphone it won't be long before the news is flooded with "Police easily bypass supposedly secure GraphoneOS"
that part I can understand. maybe release it under a different name, but they are probably not interested in that.
their code is open source, but they were so hostile with every other part of the free android community that nobody wants to deal with the shitstorm that would happen if they took patches from graphene.