Una is right, the relative profitability and probability of profitability of routes across an airlines entire network is how decisions are made. If EI or FR thought they could get a better return at ORK than SNN, KIR, DUB, LHR, wherever then aircraft and crew would be allocated. Similarly the likes of LH, SAS, SWISS and Turkish Airlines have had ample opportunity to launch connections into their hubs but choose not to, despite a range of aircraft sizes.
You'd imagine something like an E190 with 100 or so seats would be ideal for Cork, but the reality is that seat-mile costs for an E190 are roughly double that of an A320, as per JetBlue and USAirways filings with the US FAA. I think the number of profitable routes that could be flown with such an expensive aircraft would be very limited indeed and probably have the volume to cross the break-even point on an A320 anyway. It's a shame because there are routes from Cork that could use a 100 seater, but this generation of jets just aren't suitable when competing with FR.