If my trades lose, they keep the money. That's the business model - most customers lose, and they know it. No different to a casino.
Also, just like a casino, anyone who makes a consistent profit may find themselves somewhat unpopular, especially when it comes time to withdraw funds from the account.
I made the mistake of using one of these companies some years ago. In hindsight, it ought to have been obvious. Deposit money anytime I liked via electronic means. Fill out some forms, send emails and wait for processing if I wanted to withdraw. Pretty obviously they aren't expecting too many withdrawals, and are manually keeping a watch on anyone who does make a profit.