The UK loco's U2/LS etc, happily serve AMS from the various British regionals without any codeshare or interlining baggage to weigh them down.
But the British regionals have much bigger catchment areas. Waterford city has less than 50,000 people living there.
From experience, for such a short flight, Shamrock ORK-AMS fares verge on the rediculous at the best of times, particularly at weekends
The reason fares are so expensive is because of the high charges at Amsterdam. The taxes and charges alone on a return flight from Cork amount to over €63. As for fares from Waterford and Galway being cheaper, fares from both airports to Amsterdam start at €80 one way. Fares from Cork-Amsterdam start at €29 one way!