Although the MEM passenger terminal is not great, the airport itself has remarkable infrastructure. I believe MEM has 4 runways, maybe more. Few airports have as much capacity. This is because of Fedex, but the airport's ability to handle traffic without delays is exceptional.

One of the reasons Fedex is located in Memphis (a) the very helpful central location for package distribution throughout the lower 48 and (b) the lack of weather events that typically cause delays. MEM almost never gets snow; it's far enough inland to avoid hurricanes and tropical storms; it almost never gets fog. Essentially, all the things that usually lead to airport delays almost never delay Memphis (t-storms being the one major exception).

I also understand that MEM has some of the lowest landing fees in the country (because of Fedex, in part). Labor is very cheap in Memphis (TN has no state income tax). Simply put, the MEM airport has a lot going for it that makes it a perfect connecting-hub airport. Indeed, for non O &D traffic I challenge posters to think of a better airport that has more going for it in terms of location, no weather delays, runway capacity, etc.

But in the end, no matter how good these things are for MEM, O&D is what drives Delta's decisions. Perhaps that really is the only thing that can make a hub profitable. If so, then the future of MEM seems certain. (Though I still don't understand why O&D is the major thing, as many people must connect. And ATL just doesn't seem like an ideal connecting airport anymore, too crowded, congested, and delayed. But then what do I know?)