There are several stories in publication on this. Wikipedia gives a fair outline.
This may be a tactic.
In their dealings with other properties (they are after all simply property dealers and have no expansive knowledge or love of aircraft) they have changed their ownership percentages to suit their war chest. They managed to divest themselves of Teesside to the local authority after threats to close and may have thoughts of doing the same here. It is notable the Peel go where UK emergency services aviation goes. Liverpool [John Lennon, once home of Merseyside and Cheshire], Manchester City [police and air ambulance], Sheffield City [South Yorkshire], Teesside [NEASU] and DSA. They have NPAS and 2Excel the ever growing suppliers of Coast Guard fixed wing. So they are not without customers and 25 year leases at DSA but the Peel empire is only partly based on aviation.
Sheffield City was closed because it was failing and was a threat to their new project DSA [when it was Robin Hood]. That wrong footed South Yorkshire but they are still there using an industrial unit.
Another hard runway down the road at Gamston/Retford is now reducing aviation in favour of car testing.... possibly because there is simply insufficient aviation there. The industry is in a state but hopefully it will pass and the people of Doncaster and Sheffield will be off on holiday again and this [like Sheffield City] will just be a bad taste.