Not really surprised. I was a deputy (jailer) for a short-time. I hated that job. Some inmates had jobs, like cleaning or cooking, or education program stuff scheduled in their days. Most having nothing to do.
For most inmates' day, you get up, eat breakfast, go back to your cell, eat lunch, go back to your cell, eat dinner, go back to your cell, and then sleep. Sometimes, there is rec time, you get to meet visitors, or professional visit from a lawyer or po-po investigators. So back in the cell, you have a general area, at least in my jail and all the inmates did was read, watch TV, play chess, draw pictures, write letters or in their diary, or workout. Workouts involved walking, push-ups, sit-ups, curls with books, calesthetics. No machines, no weights, no pull-up bar (for suicide prevention reasons).