When poor people in my country enter prison, they become employees of the wealthy inmates. So, they don't have money to gamble. At most, if they do have money, they use it to buy cheaper phones to continue communicating with the outside world.
What happens is that prison is like another world , with other rules and everyone is looking for ways to survive, It's like entering a jungle where, if you manage to get in with the right people, you get protection, money, and even luxuries But if you don't know how to navigate that world , sometimes you end up dead There, you have to know how to be a politician. It's something that may seem Difficult to us, but that's how it is.