Once they build up the "tourist infastructure" i.e Sandals builds some resorts down there the capacity will pick back up. Most people probably don't want to jump though hoops of getting a visa and dealing with that whole process just to stay in a typical Cuban hotel that hasn't seen a renovation since 1968. As soon as this place turns more so into the DR, flights will pick back up. They probably figured there would be more "historical site tourists" when everyone just goes to the islands to drink.