You'd have to guess that Irish Rail are seeing significant loss of intercity traffic to the multitude of intercity bus services operating from the airport. Currently there are very few destinations in Ireland where the bus beats the train on time from Dublin airport and none where the train wins on cost. Maybe Tralee and Westport work better by train. So if they can steer transport policy towards the notion of direct intercity services from the airport, that suits them better.
Metro North has the usual major flaw in Dublin transport. The current plan crosses both the Sligo line and the route from GCD towards Kildare yet there is no intention to provide easy interconnection to either. Why do we keep doing this? And what's the chance of fare integration? Ah, sure you'll be able to pay twice with your leap card.
I don't think there was a lot of traffic there in the first place. The thing that's driving the success of such routes is pricing. Running Intercity services is a flawed vision and the recipe for disaster for minimal gain as the bus would still win by a mile and the cost.
If the infrastructure director and management put as much attention into securing funding to improve what we have and bring it up to decent standard we would all benefit.