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.
A casino that has a very high wagering requirement only for the deposit definitely wants its gamblers to lose their money before they can request a withdrawal because if that wasn't their purpose, they would simply keep it to 1x because, after all, it is their own money if they are giving a bonus on top of it, they can ask for any amount of wagering requirement for that and no one would have an issue.
Most people probably stop gambling at such casinos after they make their first deposit and see the wagering requirement because it makes no sense to just deposit your money and lose it only by trying to complete the wagering requirements so that you can withdraw your own money.