Trade secret from someone that worked at a Kroger in high school:
A lot of customers assume that the back room is kind of like a less-customer-friendly version of the front of the store. Like, there are some sort of shelves with dedicated spaces for specific products. That is absolutely not the case. The back room is basically a small warehouse with lots of shrink-wrapped pallets full of random assortments of foods. Like, the full load is whatever the store manager ordered, but the shipper didn't put any thought or effort into grouping like-items or anything. It's just arranged by what made a reasonably full and stable pallet. It's less like a store and more like the warehouse from the end of Raiders of the Lost Ark.
I learned quickly that, instead of explaining this to customers when they asked if we had something in the back, it was much easier to just tell them "I'll go look." Then I would walk to the breakroom that was also in the back, chat with whoever was in there for a second, then come back out and tell the customer that we didn't have it.
It's not that I wasn't willing to go to the back and get something for them, it's just that it wasn't really possible to do so.