Because Amy and Curtis are far more popular with the other islanders.
Anna and Ovie - Anna's really close to Amy, Ovie won't have a preference
Maura and Marvin - Maura will want Curtis to stay
Tommy and MM - Will both want Amy and Curtis to stay
Michael and Joanna - Michael is closer to Curtis
Anton and Belle - ...hmmm, think they may vote to save Lucie
Neither L&G nor A&C are in a couple now, so they're on equal footing in that respect