At an online casino you have no control over your own money and your own payout. A casino can come up with all kinds of reasons to prevent you from paying out, and can do anything to delay your payout. There are plenty of examples of casinos that have done that. In a real physical casino you always get paid, you don't have that problem there. But the threshold to gamble online in a casino is of course also very low, and you can go there at any time of the day. the largest amounts are therefore put in and paid out one by one.