You unlock players by buying "card packs" that give you random players, some better than others. The hope is that people will see that you are more likely to win if you spend money, then spend more money themselves. Activision has a similar patent. Here's the summary of it[1].

> The system matches an experienced player with a novice player to encourage the novice player to make purchases of items used by the experienced player. A novice player may wish to emulate the marquee player by obtaining weapons or other items used by the marquee player.

[1] https://www.sciencedirect.com/science/article/pii/S074756321...