Perhaps the status of that island might have something to do with the selection of the Irish Air Corps for this particular job?
"Aid to the civilian populace" has always been the raison d'etre for the helicopter unit within the IAC, be that SAR, air ambulance, aerial fire fighting or rescue during severe weather events (snow, flooding). I guess this operation falls into that category. Presumably the government felt there was some political gain to be had from solely employing state assets in this job and so it is doubtful that any tender was issued for this work.
The Office of Public Works (OPW) are charged with maintaining the facilities on the island and given that they are a state body, they presumably hatched the plan for this job, including IAC involvement. I'd guess the IAC undertook the work because they were ordered to do so by someone in the Department of Defence. It is doubtful too much consideration was given to using a commercial helicopter company but responsibility for that decision probably doesn't lie with the IAC.
A little more info here.
Essential renovation works to begin on Skellig Michael - Environmental News | The Irish Times - Sun, Dec 01, 2013
500 Fan.