What does Dublin have over Belfast… Very little when you think about it.
Well lets see, Dublin has a substantially larger population, Dublin has a much larger immigrant population (who want to fly home for visits), Dublin is a much bigger tourist destination than Belfast, people in the south are on average a lot richer than their northern counterparts and can afford more foreign trips, Dublin Airport is far more centrally located for accessibility from all parts of Ireland than Belfast, as well as having feeder flights to every single Irish airport bar Waterford and Belfast, and finally airlines operating from Dublin don't have to pay £10/€15 (or up to £80 on long haul flights) to the government for every departing passenger. Belfast will grow but neither airport will ever seriously challenge Dublin. Those who think it will are deluded. And before anyone says I'm biased I live in Cork.