Pretty sure it’s a fixed amount to the publisher/devs for unlimited licenses during the free period, but varies by popularity of the game, according to documents from the lawsuit against Apple

Mitch McConnell’s one principled vote of his life

This is an empirical question that people are baselessly speculating about from the armchair, when we’ve know the answer for years. Even the neoliberals over at The Economist think it’s a good idea.