Why Airlines Are Running near Empty Flights

I often wondered why airlines make journeys with nearly empty flights

I saw one today where there was only one passenger on board

Now i realise

There is a so called ''use-it-or-lose-it” rule under EU law, states airlines must fly 80% of their flights on a slot in order to safeguard their presence at major hubs for the next season

So despite losing thousands each journey they have to fly despite a lack of passengers