To avoid posible use of gambling platforms as means to launder money by simoly depositing and withdrawing and this have lead gambling sites to come up with at least a 1x wager requirement on all deposits. This law is included in all T&Cs&C of the casino and if you care to read through it you will discover them.
1x is fair, but OP's concern is that the gambling site he used requires him to make a 5x wager of his money. I agree that this is a significant requirement, and it seems like the site wants their gamblers to wager more, thereby decreasing their chances of winning. Just imagine being lucky and satisfied with your winnings, but you haven't met the requirement yet. Then, with one wrong bet, you could lose all your money. That would certainly be disappointing for any gambler.