Most probably from the intial fees/payments/buying sneakers from new users.

It seems to me like they treat (good) US$ as peanuts:

>When I started playing, I bought about $12,000 of sneakers.

Then, not entirely unlike gym subscriptions, there will be a number of people not actually using/playing the game.

Overall and loosely, besides all the complications, sneakers, resilience, average speed, whatever, it seems to me a lot like betting, you deposit a certain amount, then you choose a number (or a horse, whatever) and sometimes you win (if you are lucky and good at the game), sometimes you loose, at the end the house always wins.

It's a total pyramid scheme. But it is somewhat interesting (in my opinion) because it incentives a behavior which is beneficial for its users (getting exercise).