It is interesting to note that this casino had no licence and wasn't recognised by the Nevada gaming authorities but the inmates ensured there was no cheating there by creating a self policing system.
If you consider that prisons are meant to be there as a form of punishment, in some cases for extremely sick and serious crimes, then finding new forms of entertainment for prisoners is not exactly going to be on the top of the ideas that the public will support. In fact prisons actually actively try to stamp out the small forms of gambling that prisoners try to get away with because it ends up creating debts and some people create debts they have no intention or even ability to play off. What would prisoners want to do more of after a day of officially sanctioned gambling? Continue it back in the prison block - they have very little else to do to fill their time anyway.