I haven't been to prison but lately I have got this ability (I don't think, it's right word though) where I am able to understand why people do what they do so yeah, I can deffo understand people gambling in prison, I mean with boredom they probably have there, they have to find some activity.
Even at home when we have rain and outside activities are stagnant, we friends gather and play cards.
...
but gambling, even tho is prohibited, is often what entertains most prisoners.
Gambling with nothing at stake shouldn't be prohibited, is it?