@gigiz it's more due to the fact that Ginny's last act was delivering the baby into the world, and Kuma loved her and vowed to protect the child she left behind. Also although she's not his "real" daughter, he raised her, loved her and sacrificed for her, he is her father
Some of us have adoptive family, you piece of trash. If you can't empathize and don't care about found/chosen/adoptive family themes, then go read another manga of shut up because this has always been a main theme in One Piece.