Warmth and humidity are certainly enemies of food storage, that is for sure.Humidity seems to be a big factor. The plastic wrappers aren’t impermeable. That and/or just a difference in the local microfauna would be my guess.
We had a backup “collection” of vintage doughnuts in another building. The HVAC went out over the weekend causing it to become warm and very humid for a few days. A doughnut that had been added a week or so earlier got moldy. The older specimens were already sufficiently dry so they survived unscathed.