I don't know, but maybe the requirements of Brazilian charter operators may be unacceptable to Brazilian tour operators, and the Dominican company offered them a better deal? Why, then, almost all of South America send their tourist via LAN, Copa and Taca?
Also, from a business point of view, filling a Boeing 767 or alike might be difficult every week or so, for one tour operator. So a Dominican company (maybe with Brazilian ties?) does a wet-lease and offers the plane to various tour operators. A tour operator needs to sell packages and have seats available, not worry about spare seats selling or seats going vacant.
As a saying in aviation goes, once the plane takes off, empty seats is a lost seat.
But this is all just a speculation.
BTW, I have seen almost no charter ad-hoc or public charter services from LA, if not private jets. Maybe it's not that easy to do that in Brazil directly.
P.S. Flight Operator vs. Carrier - I don't think Dominican Media (or any general [non-industry] media for that reason) is that sophisticated to know and understand the difference. For them - You sell seats (and maybe the aircraft has even your name painted on it) - you are a carrier, basically. Wet lease, operating carrier, public charter, scheduled charter, that's far away from their understanding.
Many people fly on code-share flights and see Airline XYZ printed on their ticket and then go surprised when they board the plane and the operating carrier is not who they thought it was.
