Why? That would only be insane if the moneyhat had not already been paid. They got the money from these virtual sales, so it is all good for them.
Imagine someone lends you one million USD upfront, with no interest rate. If you earn some money, you have to give it to the lender, until you have given one million USD back and you are debt-free. If you never manage to repay the lender, then nothing happens. Meanwhile, you can do many things with the money: invest it in another project, repay your other debts (for which there are interest rates), etc.
It is even better, because the devs can earn money on other stores. It is only the money earnt on Epic store which is used to repay Tim.
The only way this can go bad is if you gamble the money, or use it for alcohol, drugs, hookers, or micro-transactions. Or if you trust a crook who takes advantage of you. It is not fee money as in winning the lottery, but it is amazing because it is paid upfront with zero interest rate.