Off topic - but I am not sure that is true in the UK/EU - did it happen elsewhere in the world?:

Before the COVID restrictions, airlines were required to use their allotted spots at least 80% of the time.[6] During the pandemic, the European Commission temporarily suspended Europe's airport slot rule for a short period.[citation needed] Due to travel restrictions, many flights were cancelled or had limited capacity, which made it difficult for airlines to fulfill all the requirements for possessing an airport slot. The suspension of the slot rule was reinstated in October 2021. After the slot rule was reinstated, the rule only required European airlines to use 75% of their flight slots for the winter season.

https://en.wikipedia.org/wiki/Ghost_flight_%28commercial_avi...