I remember reading some pamphlet they had 20-some years ago about this, they had one (or two?) distribution centers for all their stores and wanted to keep the quality at a very high level. I assume they feel they can't expand and keep things the same. Then again, maybe the owners are just content with the way things have been going and see no reason to expand.
I mean, they're in Dallas and Austin now. They're definitely expanding quite a bit.
They don't freeze their ingredients so it all has to be super close by to remain fresh.