Whole Cake Island makes you care, and that is why the Whole Cake Island arc is wonderful.
So I guess that’s the biggest reason to keep up with One Piece if you may have dropped out of it – Whole Cake Island forces you to not look at these characters as typical protagonists, but as people that might get stomped to death by Big Mom.
They both have stuff in common – they begin in the wake of Luffy and Luffy’s punches freeing a kingdom from an evil warlord (as he did in the Alabasta and Dressrosa arcs), events are set in motion after a crew mate abandons the Straw Hat Crew (Robin in Enies Lobby, Sanji in Whole Cake), and they deal with the crew facing near insurmountable odds (In Enies Lobby, the crew declares war on the World Government, and Whole Cake Island is owned by Big Mom, one of the Emperors of the Sea.)