Surgery removes polyps. But it doesn't remove the swelling that caused them to grow in the first place. That's why polyps can come back, even after a good surgery.
Think of it like treating a skin flare-up. Clearing the flare doesn't cure the tendency to get it again. It's the ongoing care that keeps it under control — not one single treatment.
Keeping up with nose rinses and steroid sprays after surgery lowers the chance of polyps returning. For harder cases, biologic medicine adds another layer of long-term control.