It’s like every other business in the world. If you owe them money or buying something from them, the world is your oyster with everything setup in a way to make that transaction as smooth and convenient as possible.
Now if you are asking for a refund or a withdrawal in this case, you have to jump through many hoops and go through hell to get your money back.
In the case of
gambling sites, they are also banking on the psychology of the average gambler meaning that with the passage of time, the temptation of going to gamble more either to win more or to make back previous losses, increases by many folds.
As someone above already said: the casino *always* wins because the system is just setup that way.