Maybe for a special event, or a major holiday, seats don't generally sell out. Even then, airlines would often create additional capacity if they are seeing higher than normal demand.

At this point for October tix, most fares have not been filed yet, so you are seeing some of the higher fare buckets by default. For example, I pulled up some random dates in October, and lots of C & D fares while cabins are wide open. You are not going to see lower rates until United files additional fares.

Generally speaking, airlines are in no rush to file discounted premium fares far out because they have data points in consumer buying behavior.