The DR is squarely focused on tourist visits, the majority of those during the winter months. The airlines can fill planes during these times of higher demand and cannot during the off season. Thus flights do not come on a regular basis during the off-season from many countries.
It's unfortunate, but another example of how the number of residents wishing to fly to Europe from the DR is insufficient to maintain the interest of any airline (apparently). Canadians see the same trend for flights to/from Canada and POP. The bulk of the interest is prepaid vacations to PUJ so that is where the majority of the direct flights are scheduled.
While not yet as limited as flights to Europe, I foresee the trend of Canadian <-> POP flights dwindling until they too become nonexistent for much of the year. At which time, North Coast resident Canadians will need to reexamine how important it is to live somewhat close to an airport that can get them a flight home when needed.
The DR is not promoting itself as a year round retirement destination in Europe and North America so expect the number of residents to remain fairly low for the foreseeable future. Thus the availability of year round flights to far away countries will be limited and inconvenient for much of the off season. The choices seem to be leaning towards planning to travel home during the tourist season or flying to the US and then catching a connecting flight to your ultimate destination the rest of the year.