I also believe that greed is the main reason for major losses in gambling. The unwillingness to let go of something you’ve already imagined as yours leads to reckless actions and risks you're not prepared for. And by the time clarity comes it’s often too late. That’s why it’s important to have something or someone who can stop you in time, remind you of your limits, and bring you back to reality before the thrill of gambling completely clouds your judgment.
Greed and for those who wouldn't let go of their losses, having greed of making large profits is a reason why gamblers lose a lot but there are some also who gamble without greed but hence don't like losing all deposits to the casino, this set as well often hits greater losses because what can't be changed is that the casino is meant to do better than gamblers and only way out is for gamblers not to chase what was lost.
Although there are times you have to be greedy to get a mind-blowing win, so I don't really blame some of the gamblers that do express such greed which do later take all they have managed to win as well as their own pocket money they started with. Maybe if they can try to manage their level of greed and not go too extreme with it then they might have to know when it's the right time to leave with the little you have and try again the next day in within your affordable risk amount.