Probably because of McCay, the schizo who's on the board, and his personality of attacking figures like Rossmann and Techlore. Lineage supports older hardware, and Calyx is a beginner's Graphene, but without the Graphene implementations and security structure. 

 Agreed. I appreciate their amazing work but their main dev needs help. I hope the best for him and the project.

Just to be clear, I love and support GrapheneOS and hope their dev receives the help and support he deserves to take care of his mental health.