Buses to terminal on arrival

[davidjohnson6]

Sometimes when arriving at an airport, the aircraft has parked at a remote stand, and there has been a need for buses to transfer passengers to the terminal. For an A320/B737 sized aircraft, typically there will be 2 buses, with passengers able to choose which bus they board, and someone marshalling passengers onto a bus to ensure they don't go wandering off.

For some reason, it seems to be necessary to wait for all passengers to come off the aircraft before either bus can depart for the terminal. Why is it not possible to let the first approx 90 or 100 passengers onto the 1st bus, send the 1st bus to the terminal, and then let the remaining passengers, who need more time to transfer from aircraft seat to bus, board onto the remaining 2nd bus ?

For the passengers who are more mobile, there would be less waiting around, immigration staff can begin processing passengers a few minutes earlier instead of looking at a non-existent queue, the airport can reuse a bus slightly earlier (or be ready to collect the passengers at the terminal waiting to board the aircraft a little earlier which would reduce aircraft turnaround time), and the driver may get to go back to chat to his/her colleagues slightly earlier.