That half a mile is needed for non-negotiable constraints, like the scale of airplanes (e.g. gaps between landing strips or fingers), the capacity targets (walk

That half a mile is needed for non-negotiable constraints, like the scale of airplanes (e.g. gaps between landing strips or fingers), the capacity targets (walking to board a plane is better than not flying at all) or the available space to add terminals (Heathrow is a good example). There are also practical needs, functions that follow the form, that are no less important than minimizing walking, like the convenience and cost reduction of putting a lot of travellers in the same huge terminal and if possible in the same huge hall, with one subway station, one customs funnel, and so on.