Maybe they go out to eat.
There was a time in my life when I rarely ate anything at home.
I worked midnights at the hospital and would eat something there in the cafeteria
about 1 in the morning. Then at 7 in the morning I would go back down to the
cafeteria after I clocked out, and grab breakfast to go which was usually an egg
biscuit. Then I would drive home, take a shower, go to sleep, get up a few hours
later and go to classes. After classes, I would often pick up a salad at a nearby
grocery store and a brownie at the bakery next door. I'd get home, eat and go
to bed. I'd then wake up and it would be time to start all over again.
So maybe that is what they do. They may not buy much in regards to groceries
because they may not have time to eat at home.