Its a very common terms on most of the gambling sites because they run promotion to attract players and make money from them so they will not give any advantage to players who just came here with free roll or whatever which happened for real, its not scam but not fair so its your decision now whether you want to deposit some money and take out the winnings or just let it there forever.
Name any reputable poker platform which require you to deposit and generate rake equal to five time your tournament winnings and I will keep silent for ever. The thing is hat it is plan scam and if I will not expose they will carry on with these type of things.