1, time constraints: takeaway riders usually need to fulfill multiple orders within a specified time, so they may deliver the food as soon as possible and knock on the door once in a short period of time.
2. Avoiding interruptions: Takeaway riders may think that they can get a customer's attention with just a gentle knock on the door without having to unduly disturb the customer.
3. Be courteous: Delivery riders may believe that knocking too often or strongly may cause unnecessary disturbance or annoyance to customers, so they will usually be appropriately courteous. In short, takeaway riders knock on the door only once for reasons such as delivering food as soon as possible, avoiding disturbing customers and maintaining politeness.