With all due respect it's about the catchment area of OST rather than just about the airport and the city of Ostend itself, and that catchment area includes Bruges and, as others have mentioned, the Flanders coast and if one should dare to pour scorn, be negative, regarding some of these weird and wonderful route ideas that appear on Airlines, Airports & Routes it seems the spotter fraternity are waiting in the wings ready to attack.
Belgian as a whole has five functioning airports serving four cities, Brussels, Antwerp, Liege and Ostend and of these Liege and Ostend only have leisure routes, that is Belgians going on holiday rather than foreign tourists coming to Belgium. Antwerp has one business route to LCY, BMIr tried a business/leisure route to MAN and failed, other than that ANR is also a leisure route airport whilst Brussels provides for much of the country with Charleroi being the LoCo airport for Brussels, despite the country of Belgium stretching much farther south there are no functioning airports south of Charleroi, basically Belgium is a country that not that many tourists want to travel to when compared to other European countries.
So there are two functioning airports in Flanders serving the Flanders coast, OST that Ryanair tried to serve and failed and ANR that BMIr tried to serve and failed, what would BMIr's aircraft type have been, a 50 seater Embraer pocket rocket?
So suggestions that a route from northern UK to Flanders would be viable with a 70/80 seater aircraft, well history suggests otherwise!