It's actually a very clever therapeutic program. The prison is a maximum security prison where 70% of the inmates are there for murder. Most of the people in the cat program have always been animal lovers, despite their complex human relationships.
The inmates attest to how much they love their cats and how the animals have helped them calm their anger and give them positive responsibility. The inmates cannot keep the cats if they get in trouble, and it has helped the inmates control how they express their anger. They now have something to lose if they lose their temper. Many of the cats come from the animal shelters in the area, so it's good for the cats too!