The final destination of divert doesn't solely end with EI, there are many other factors to take into consideration. Can ground handling be put into place at short notice, if the ground handler doesnt handle EI anywhere else it is hard to put in place details where the airline can be charged.
But other airlines including a few flag carriers on many of those occasions had exactly the same problems regarding handling agents, but they still landed at much nearer airports and got their staff in their home country to make the necessary arrangements if it could not be done by staff at the airport.
Other factors are can the airport accommodate the flight at that time, if there are numerous aircraft diverting, say an airline that is already based at the airport that airline will get preference to landing and precious ramp space for aircraft. Re-fuelling contracts is another factor - does the airline have contracts with the company that provides refuelling so that the aircraft can leave again.
Well I know for a fact it was not the fact the airports could not take the diversions, because as stated previously, on all of the occasions I, or my friends were diverted to Berlin, EI flights were the only flights diverted out of Poland and the crew on all occasions made it clear such decision was being taken, on the basis that SXF was a regular EI airport and this is the basis on which diversions are made. On one occasion they tried to pull the wool over our eyes by declaring that all airports in the country were closed whilst on a friends flight they claimed that other airports were not able to accommodate A320's despite Wizz Air among others were landing exactly the same aircraft.
I get that u have been annoyed and frustrated as its not nice for anyone to land at the wrong airport but there are other things to consider and its just not as black and white as you make it out.
It's pretty black and white to me and most of the other passengers who were diverted. The fact is problems regarding fueling arrangements, transport and handling agents could be sorted out but they may cost money and cause someone in Dublin a lot of stress. But it seemed that it was much easier to palm the passengers off to a handling agent so it became the problem of someone else.
The point I'm trying to make, is yes, there were obstacles and problems to overcome, but it would have been nice if they did try to overcome them, rather than just palming off to the handling agent at first opportunity and cause the passengers to arrive at their destination nearly 18 hours later than originally planned. It's not good customer service and I expected better from Aer Lingus. Easyjet, who incidentally have the same fuel supplier at Krakow Airport and the same handling agent, were able to divert to Katowice and Krakow is the only airport they serve.