As an EWAG, I would say it may be pure economics - supply vs. demand.

However, another thought would be the rural mentality that, unfortunately, still exists in the OKC metro area - "11 o' clock? Now why would anyone be up that late?"

With the price of fuel, it likely wouldn't be cost effective to run a regular schedule of trolleys until late night. Perhaps the motels/hotels in the Meridian corridor could work on that as a group? It would certainly benefit business!