Ghost flight and European Union, what's the deal

As you are reading this article, thousands of planes are flying empty due to EU rules. Indeed, According to the airline Lufthansa, the carrier company will have to operate 18,000 empty and polluting flights or "ghost flights" this winter. Why is this the case?

What are ghost flights:

Airlines taking off from the continent must use 80 per cent of their slots or lose them to someone else. This means airlines continue to fly planned routes regularly even though there are few or no passengers at all on board, costing money and emitting carbon emissions into the atmosphere. Failure to do so means they forfeit the slots according to EU restrictions. (independent). What is happening then:

Lufthansa Group, the parent company that owns brands including Lufthansa, Swiss International Airlines, Austrian Airlines, Eurowings and Brussels Airlines, made headlines after admitting 18,000 flights would be flown empty this winter, including 3,000 Brussels Airlines services, due to the ‘use it or lose it’ airport slot rules. What are the consequences: This occurs In a context of a pandemic where a 50% loss in global air passengers in 2021 (compared to 2019) and where air travel accounts for about 2.5% of the global CO2(eq) emissions. In March 2020, The Independent reported that, during the coronavirus lockdown, Ryanair still appeared to be flying most of its fleet regularly. Why are these rules in place:

These rules aim to ensure the aviation market is competitive by incentivising airlines to fly, trade or hand back unused airport slots. Planes that have been grounded for a significant period have to be checked over before they can fly again, a time-consuming process that costs the airline money. The critics: “We know that the airline industry puts profit ahead of people and the planet but the absurdity of ‘ghost flights’ takes its recklessness to new heights." “Flying no one to nowhere for no reason other than to keep runway slots is absurdly polluting and wasteful." Greenpeace UK's policy director Doug Parr