Nobody can say why people don't stop playing casino even when they lose. People know that they lose money even they know that they do not have money at all because they have lost all they money but they continue to play casino. They take credits and do not return the credis but they continue to play casino.
Casion is magic. People continue to play casino. That is why casino so popular and theire are so many casionos.
I can say, due to addiction, people can't stop casinos. At the beginning of starting a gamble, people think it's a quick money-making method. Most probably they are witnesses of someone winning a big amount from the gambling somehow. And they start thinking about making money quickly. As a result, if the luck doesn't favour them, they start losing. So to recover the loss again, they play, and it continues this way.
Sometimes they win, and it does raise a hope for a big win. That's how they become addicted to gambling, and eventually they can't leave gambling. If people left gambling, then casino businesses wouldn't run longer. Also, that's the reason casinos often offer promos in different ways. It does make people more greedy as well.