We try to make things as simple as possible which means, instead of having to customize each airport just to say "no" to the passenger bus, it would be much easier to simply have the passengers deboarding as a separate menu option so, if you don't want to call the bus/stairs, simply don't call them.
Of course, this will allow better flexibility, because you will be able to call bus/stairs anyway, in case you want them, without having the de-customize the airport.
