Shannon is pretty much in thr same boat, with an even smaller population within a reasonable travel distance and no rail link. Ryanair has dallied with Shannon for years increasing then decreasing routes. The Shannon stopover rule for airlines serving Dublin from North America was first relaxed, then abandoned and the airport should have died at the time the traditional trans Atlantic traffic VFR traffic was dying.
It survives because a good number of leasing companies are based or have their European operation at or near the airport. This brings in aircraft for parking. In parallel, aircraft maintenance and repainting provides constant business and employment and Shannon, US forces treansport aircraft are regular visitors and Shannon is better placed for emergency diversions off the Atlantic than Prestwick given the average positions of rhe North Atlantic Organised Track System throughout the year.