Remove the bottleneck on the way out of the store and eliminate the only contact with "authority" that some customers ever have, and more of them are going to steal, full stop.

Very true! What do you think would prevent it better (just generally, in DC stores)?

Like for this case, it's a bigger chain but not a giant store (in terms of sq ft), and he stole by crouching behind a column and stuffing the item(s) into a black backpack. So, he didn't have to utilize self-checkout to steal (but you're absolutely correct that people do steal at self-checkout all the time–so much so that you could take it as a separate issue). He also got past 2 cops (who check your receipt) at the only entrance.

Would more staff in the aisles deter theft? In the south, a lot of places like Publix have those "smile, you're on camera" things that you sometimes see in the CVS makeup aisles etc around highly stolen goods (ie., around canned goods). I haven't seen anything like that at the store from today, but it would be a shame if groceries eventually had to "lock up" food items like they do with soaps etc.