Why do my genital warts keep returning?

It depends...: If this is happening over a few weeks or months, it's probably nothing special. Just keep treating them, or see a doctor for in-office treatment, maybe with cautery or freezing. They'll eventually stop recurring. If it's happening over more than a few months, it might not be warts; although such late recurrence can happen, it is uncommon. See a doctor to confirm the diagnosis and for treatment.