I know that's the marketing strategy that most casinos do here in cryptocurrency. But from another angle, if we look closely, the bonuses they supposedly give, in fact, also come from the amount of the depositor who gambled.
For example, other casinos say they will give a bonus of 25$ to those who sign-up on their gambling platform, but before you can get the bonus of 25$, you must first deposit an amount of 500$ on their platform. Do you think that the 25$ will come directly from the owner of the gambling site? of course not, instead the 25$ bonus in reality will come from the gambler's money. It's a bit tricky to get there.
I would say that not only the bonus the casino pays us, but also the winnings we make are coming out of the pockets from other gamblers. A new casino always needs a certain amount to start with, to cover potential winnings and withdrawals. Eventually the casino will start using revenues to cover outflows and be able to pay dividends to the owner. Running a casino is not free, they need to maintain the servers, pay for electricity and employees, pay for a gambling licence, keep upgrading their IT security and run advertising campaigns. With all that in mind it should be clear that a casino needs to make a profit each month to function. They achieve this with having games that offer a house edge. That's why the number of losers will be higher than the number of winners, but this doesn't mean that we can't make a profit gambling.