Such casinos usually use gamblers as a tempting bonus, if a gambler deposits there and the gambler directly they will not be able to use that deposit bonus. This is true because it is better not to enter such gambling sites, and if you accidentally create an account on such a gambling site and deposit, you will be hit repeatedly and you will have to lose your money intentionally.
And if the money you deposit and gamble or win at the casino is more than the original balance, you will have trouble withdrawing it and will repeatedly throw you into confusion. So it is best for everyone to be careful of such gambling sites, and it is better to use trusted gambling sites.
I don't know which casino the OP is talking about, but what did you expect? To receive free money just by depositing? I don't think this necessarily makes the casino "bad"; I'm not blaming the OP here; we've all fallen victim to these so-called bonuses. These bonuses are rarely what they seem to be and usually have fine print on how they're distributed. In this case, it's a cashback bonus on your losses. I know it's not worth much, but at least you'll receive something back in case you've lost, which you can use to make a few bets or play a few games again.