Possible reasons: a Dynamic Delivery Price row (set by cart subtotal) is triggering a $0 rate; the route has Charge only one fee per day of pickup? turned on and the customer already has an order for that delivery day on that route/zip; a coupon or promotion with free delivery is applied; or delivery fees were disabled for the order (e.g. an admin-created order). Open the zip entry to review its Dynamic Delivery Price rows, and check the route's toggle and any active coupon.