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.
I agree the promo terms where you're forced to roll it over is very common but not all sites require you to rollover the reward 5x.
From my experience the usual rollover on most sites is very low like 1x or maybe 2x at best.
Yes, the amount they are asking is too huge but it maybe their strategy and its their terms which is also same as nitrogensports if I am nit wrong then why OP wants to win a promotion from them when they have such greedy terms favours them more.