Seller doesn't have item but keeps it listed.

I'm trying to find the logic behind this:

I ordered a camera lens and after getting a tracking number it didn't get any shipping updates. It was a Choice item so after a while I got a $1 return for them not meeting the delivery deadline. Of course I messaged them what was going on and then yesterday all of a sudden they cancelled the order and I got a refund.

I asked why and they responded they didn't have the item so they refunded. However, it's still listed in their store.

I'm trying to understand why they just don't mark it as being sold out. People can still order it, they can't ship, people get a $1 refund and in the end the order gets cancelled and they have to refund and most buyers will give them a bad rating. What's their gain?