It also can bring players back to the game. Like what Blizzard is doing. Maybe you quit playing their game, they are offing you to buy sub tokens in the games launcher so maybe you don't want to pay monthly anymore but have a few million gold saved up and are willing to let another person foot the bill for your currency. You can play the game again and the company gets another active account by someone else paying for it.

Sub tokens are great for people who do not have a lot of real life money to help pay for the game.