The gist is that they make money by a) selling a monthly subscription to give you more options and features, and b) charging you the amounts too small to motivate you so you can get up to the amounts that you take seriously.
They've set up their pricing so that you will pay half of the motivating amount to find the motivating amount, e.g., you might lose $5+10+30 over three weeks in order to find out that the threat of paying $90 motivates you. They argue that most people would never feel that $90 threat without experiencing the first $45 of losses because they'd either not sign up for $90 right away or cancel quickly since they hadn't sunk anything into the program.
Their more experienced users pay the monthly premium to skip the first few weeks of penalties and make progress faster since they already know the level of financial risk that motivates them. They also let you adjust the number down since circumstances and habits can change your ideal wager.