Originally Posted by A_Lee

The bus thing happens all the time and it has absolutely nothing to do with gates at the terminal not being available. It's simply done when the arriving aircraft is not going to turn around and fly out with passengers boarding from the same gate. Much of the time there's no rhyme or reason to which flight gets a bus, as their aircraft rotation isn't fixed. As mentioned, it could be the aircraft is switching between an international and a domestic flight. It could be the aircraft won't be used next for many hours and all the gates will be occupied before that time. It could be the aircraft is going in for maintenance. Etc. If they use a terminal gate, it costs them money that the airport charges for the gate. If they use a remote stand and their own buses, it's cheaper. That's why they don't want to use a gate if the aircraft isn't doing a turnaround.