The aircraft doesn't move until they say it's ready.
Ground handling agents turn aircraft around between flights. Bags loaded and balanced. Catering restocked. Fuel uplifted. Passengers boarded. Ground power connected and pulled. Steps positioned. Doors armed.
At a busy airport, a turnaround runs to under forty minutes. Every one of those minutes is choreographed.
Airlines sell seats. Ground handlers make those seats possible. Contract rates in ground handling are among the lowest in aviation, and turnover reflects it. When a turnaround goes wrong, the ground handler is first in the frame. When it goes right, nobody notices.
Every on-time departure is a small logistical miracle.
Most of the people who made it happen are already halfway through the next one before the aircraft reaches the runway.
The invisible work holds the schedule together.