My point was more why get €160 for flying someone to Amsterdam and back when you could get €600 for flying them to New York. I'm surprised they see demand as so low that the additional income isn't worth it.
I take your point. I suppose what I'm wondering is what proportion of Cork-NYC ( for example) passengers fly via LHR or AMS, and what proportion travel to SNN or DUB to fly from there. If it's mostly the former, then yes, I agree with you; if most Cork transatlantic pax are already flying from another Irish airport then the potential extra revenue from a Cork-Dublin service is much less.
DAA have the answer to the above: their passenger surveys in Dublin ( and I imagine Shannon until last year) include questions about county of origin. I don't know the answer myself so I am just musing aloud!