Thats really strange. When my friend and I went in May to the Pop, they did have AA batteries for sale, 4 on a card (I think it was Energizer), but my friend didn't want to pay $6 for a 4 pack. But they were there, they were up by the register closest to the bus stops.
It has been a few years but when my daughters spray fan batteries ran out we went to a kiosk where they sell the fans to buy batteries and they gave us some free for the fan - said it was because we bought it at the parks. They had packages for sale at those kiosks.
Maybe they didn’t get a shipment from their supplier or something - backorder perhaps?
We had the same problem this summer. We were staying at POR and searched all over the resort and parks. One night when coming back from a park, we stopped in the gift shop and asked a CM and she gave us four. I have no idea where she found them, they just magically appeared.
AA batteries are in everything these days ( or so it seems ) and with it being so hot the last few weeks they could just be out. We did see them at AKL and in the parks a few weeks ago.
We were told this too in August at the first shop in Epcot - same exact wording, so we ordered from Amazon and low and behold next day saw theme everywhere at the next park! So keep looking!