In some cases. This happened in the EU during the COVID pandemic due to weird regulatory reasons. But in general: if no one is booked on the plane, they will s

In some cases. This happened in the EU during the COVID pandemic due to weird regulatory reasons. But in general: if no one is booked on the plane, they will stop selling that flight pretty quick. Of course in the short term they might fly an empty flight if all passengers no-showed and if they need the plane at the other airport, but their fleet allocation optimizer probably works at most a couple days ahead, so empty flights will soon be culled. Similarly routes with few passengers will get allocated smaller planes in the future, etc, etc.