Why tax free shops in airports do not sell goods to passengers going to domestic flights?

I am Brazilian, and in Brazil, as well as in most Latin American countries, the Duty Free shop in inside International Departure/Arrivals area, so it's impossible to get there in the case of domestic flights. I have lived in Germany, and how domestic and international flights (In Europe it's hard to separated domestic and international, because should be considerated if the country is Schengen or not) depart, most of the times, from the same hall, the Duty Free is accessible for both passengers. I remembered that most itens were duty paid, except for cigarets, destinated just for people fighting outside EU. Also they sold duty paid cigarets. I don't know why this shops are stil called Duty Free, because just few itens are indeed duty free (I remember just cigarets).