Aer Lingus is after all majority owned by the Irish taxpayer and Ryanair.
Whilst in theory everything you say would make sense, Aer Lingus is now a plc and not a state owned airline anymore. It may have shareholders in the Government and Ryanair but it also 45% owned by other parties. Aer Lingus are generally staying quiet on this and so they should be. Right now they are the legal tenants of the hangar. It is not for them to comment as they can't be moved unless their lease is challenged in the courts. If the DAA exercise the clause in removing them they could potentially be sitting on a gold mine. They will then have 12 months to move and that's after the legal wrangling takes place. They can also enforce the clause in insisting they move to a hangar of similar size to be built by the DAA. This will delay things even further. The board of Aer Lingus won't bow to pressure from Ryanair to move without a significant financial payoff from some party, and nor should they. I would expect the same if the situation was reversed and Ryanair were occupying it. They are a business not a charity and by moving at the present time without an incentive will do nothing to help their financial position. They did not create the problem.
As I have said before the answer to a solution in all this would be if the Ryanair shareholding in Aer Lingus was put up for sale in exchange for the hangar I believe the Mangagment in Aer Lingus would as Noel Edmunds would say 'DEAL'. Michael Cawley of Ryanair at a recent meeting said that the shares are for sale only no-one will buy them. The Government now have an opportunity to broker a deal through these means. O Leary has gone on record many times as saying Aer Lingus is a basket case with no future and will go under. He could now get some return for his shareholders on what so far has been a disastrous investment along with getting the hangar he wants for his own needs. It would certainly test how serious he is on both counts. Hardly likely to happen but a deal breaker and compromise all the same. All parties would walk away happy.