The main problem with airports outside of Dublin is they were/are always very dependent on outbound passengers and the main cuts to air services have being dropping IT fights, scheduled airlines switching from city to holiday flights to remain profitable while UK and the previous Irish tax has caused a slump in demand between UK and Ireland. The typical city breaks have reduced while eastern Europe market was always going to decline when things started to change.
When you look back, what has caused the decline in passenger numbers, airports have not lost a lot of valuable routes its just bucket and spade routes. Yes there is Ei moving over the road but aside from that nothing major has changed.
Domestic demand will need to pick up before regional airports bounce back.