just shows how gambling will always exist anywhere
Yes, gambling is everywhere, even in remote places like prisons. This is especially true for those imprisoned for gambling. In some countries where gambling is illegal, those caught gambling can be imprisoned. I don't think prisons are as strict as we imagine. They can still gamble, even if the stakes are a pack of cigarettes or anything else; even those in prison can do that.
I got to realise that gambling can be related to some activities like the one in the example you mentioned that prisoners do engage in. We keep our money for breakfast while going to school in order to use it and play dice game after school. For anyone that gets to win the dice game, will take the whole money allocated for that game. So gambling activities still take place in a more minimal level even before we get to see casinos coming up to make it more elaborate. Gambling activities resides in us from using anything valuable to us in exchange for the outcome of a game or event.