Keep in mind when the number of Americans is thrown around, the bulk are Dominican-Americans, often with dual citizenship. The typical "American" isn't the gringo type. Case in point, some of the places that have the greatest concentrations of actual gringo Americans is the Sosúa-Cabarete area and perhaps the Bávaro-Punta Cana area. If you notice, there isn't much presence of the larger Dominican companies that focus their business on local consumption in the Sosúa-Caberete area. You have to go to Puerto Plata proper to see signs of some of the larger Dominicsn companies targeting local consumption.
That area also don't have Dominican stores that are geared more to the upper/upper middle classes, despite the typical gringo American that lives in the DR has an income level that from an economic perspective puts them in the income brackets that stores such as Casa Cuesta are geared to. As large as the expat community is in the Sosúa-Cabarete area, it simply isn't large enough to support such as store. The closest one is in Santiago and they are geared 100% to Dominicans. Notice they don't even have any advertisements in English. The places where they do advertise sre dependent mostly on Dominican consumption such as the major newspapers and in Dominican visitors dominated website. I have yet to see one advertisement banner of Casa Cuesta in DR1 and this is the largest English website focused on the DR snd perhaps the most visited by expats everywhere in the DR.
Now Bávaro-Punta Cana does have a greater presence of major Dominican stores geared mostly to the middle class and up. The latest one that open a few days ago is Unido. Then you have to ask who are most of the shoppers in these stores? You do see more expats shopping in places in the Bávaro-Punta Cana such as Sirena Market, Nacional, Bellón, etc there than in their other stores in the rest of the DR. However, you see more of them, but they aren't most of the shoppers either. Then comes the issue with advertisements, all in Spanish and all geared to Dominicans. That should be another sign. You will see some real estate advertisements, especially in billboards, in the Bávaro - Punta Cana area in languages that are definitely not Spanish, but the same can't be said regarding other things. Even then, most real estate advertisements seen in the Bávaro-Punta Cana area are also in Spanish.
I have no idea what is the number of gringo Americans living in the DR, but I would be very surprise if it surpasses 20,000 and that is being very liberal sbout the figure.