I'm guessing this is in large part due to a generally low level of knowledge about how gambling (and particularly online gambling) works. At the time of my first encounter with Bitcoin gambling (Satoshi Mines) I was also quite ignorant but it took me ~10 minutes to figure out the probabilities. I'm still mystified why some people don't want to learn how gambling works and at the same time are willing to put a lot of money on their wrong assumptions. Let me know what you think.
It's not just ignorance, some people just have a tendency to think that laws don't apply to them, that they are special and have luck, and they surely will win. So, a person can understand that the odds are against them, and still gamble like crazy because of their superstition. I think this is far more common than not understanding the math behind gambling.
This is something that I see a lot in my life, people feel that somehow they are special and obviously every single human being is unique and very special for himself, his family and friends, but when it comes to the numbers we can become another statistic, but somehow people believe that it is never going to happen to them, that somehow the laws that rule our lives do not apply to them and that they can do whatever they want without any consequences only to discover that is not true.