If I ever get into prison, gambling will be the last thing I would do there. I will do my best to find a less stressful time killer and entertainment.
This prison gambling usually just fictional since they are well monitored on the CCTV by police while they are not allowed to hold money and other valuable things in the prison most importantly any gambling materials.
You might be too positive. I do not know if you are just from a rich country or you can only think of prisons from rich countries but not all prisons have cameras all around. Most likely they only have in entry and exit points. Some jails in my country literally are overpopulating and it would be naive to think that absolutely nothing illegal is going on and that the police can monitor everything.
Most of the prisoners do task depending on the country. So it’s very rare for prisoners to have allowed time to gamble among prisoners.
Maybe other games such as sports is possible in prison.
They can still gamble while playing sports themselves, can't they? That would be sports betting among them and not professional athletes but almost the same thing.