People use bitcoin because of a lot of reasons, the security of bitcoin is a very good reason.Also the anonymousity of bitcoin, pay with bitcoin since it doesn't register to any name or any personal information.
Yes that is the best reason which attract customers to use bitcoin suppose if a person want to buy some credits on a gambling site and he do not want to show his identity then he choose to use bitcoin.
Most of the users are using bitcoin for gambling as they know that bitcoin has made gambling easier as you can gamble anytime from anywhere without disclosing your identity and the best thing is that you can gamble even with a small amount.