SNN busiest year was 2006 with just over 3.7 million passengers but started to fall right away even before the economy went down in 2008 which says a lot. I don't think you will see such figures again for a long time if at all.
It's depressing I know but it's the way of the aviation world right now, in this case consolidating at hubs, then increasing frequencies
Plus, is it fair to say the 2006 peak was achieved while the Stopover regime was still in operation, and includes something like 250,000 US troop movements.
And evidence of consolidation is there. In 2014, Cork Airport had about 66% of its peak 2008 traffic, while Shannon had about 45% of its peak 2006 traffic. By comparison, Dublin had recovered to 93% of its peak 2008 performance.
Even 10 years ago, how long and inconvenient a journey would it be to see Belfast, Dublin, Kilkenny, Cork, Killarney,The Cliffs of Moher, Galway etc? Back then it made sense for tourists to fly in to one airport and out from another, now with the new road network on the island that is no longer a requirement, hence no more Lufthansa, Air France etc in Shannon.
But, in any event, Shannon seems to have closed its mind to such traffic. Recall their breathtaking pettiness when promoting the US Airways Philadephia route. The airline promoted it thus:
US Airways Brings Philadelphia Link Back to Shannon :: Routesonline
<...> said Andrew Nocella, senior vice president, marketing and planning, US Airways. <...> For visitors to Ireland,
US Airways anticipates a growth in dual route passengers with people potentially travelling one way on the seasonal link to/from Shannon and the other to/from Dublin. “Beginning next spring, our customers will again have non-stop access to both coasts of Ireland.
Customers can begin their trip with the Cliffs of Moher outside of Shannon and end it with the castles in Dublin, seeing all that Ireland has to offer,”
People in Shannon actually found the time in the course of their busy day to change this to:
Incredible to think it, but mentioning the existence of Dublin was just too much for them.