From what I've experienced, once your 10th villager moves in, certain villagers will decide they want to move. My first villager to move out was Fuschia. She and Portia were the only ones who kept running up to me repeatedly to ask. I'd tell her no, reset the game and she would run up to me again until I told her yes. Meanwhile, the villagers that I have been ignoring for weeks and hitting with nets all day long love me and being in town.