It was important to keep an eye on the Sins. Loosen the leash too much, and they got all sorts of unproductive ideas in their heads.
Envy had been unusually difficult to find, but the reason became obvious once Satan was close enough to smell him. He was damn near covered in the blood of a Virtue.
"Well, someone's been naughty," Satan remarked as she leaned against the shelf of Ramen noodles next to Envy.