Epic CEO Tim Sweeney previously revealed that the company pays a flat fee to each developer to give away their games, rather than paying per download.
Your download doesn't give the developer any money. The fee is already paid. The Developer gets just as much from you if you pirate their game, or more if you go purchase it on a different platform instead.
Tyrants of the Underdark is my favorite deck builder. The control board provides a good focus for player interaction and back and forth between them players while still maintaining a core of building an efficient deck for what you are trying to achieve.