The reason why inmates gravitate to kitchen duty is because they learn a marketable skill of how to work in a kitchen. However, they also get to sneak food to supplement their diets, which are not guaranteed to be filling.
I was a food supervisor and had an inmate transfer to the fed prison industries to make more money, a month later he transferred back to food and told me he was making 300 a month for the 8 hr. days but he was making 900 a month stealing meat and cheese and selling after hour sandwiches in the cell house