The upper part of the pit was not excavated because it could not be seen in the topsoil, was plowed away decades ago, or was lost to bulldozing to clear the site. Classic statements, but unnecessary. The answer is far simpler, but to appreciate it one must realize how significant the late summer and early fall were to the Indians. During the late summer and early fall, the majority of storable food resources mature or become available in the Upper Delaware Valley. The fall is the time of great abundance, and the people would had to have taken advantage of everything.
Diversity is still the key to survival.
No one crop, animal, or resource can be depended on to get them through the winter and early spring. They have been living on the floodplain for several months, possibly even tending maize plants, but now they are getting ready for one final push before they leave. Once the processing was underway, there would be no respite. Small groups of collectors, hunters, and fishers would be returning to the processing camp on a daily basis with their fresh food and kill. All this would have to be processed quickly before it began to decay in the late summer heat and humidity.