I am guessing that the reason for a locomotive on each end is the train is too long to turn at the Event Park Wye. Either the tail is too short for the train or the train is too long to fit between the switches on the mainline. We had the same problem with Polar Express trains at the Texas State Railroad. In our case, a diesel went on the east end and the steam locomotive went on the west end. The train was a couple of cars too long to fit between the switches in both Palestine and Jarvis Wye.
Additionally, you save quite a bit of time by not having to turn the locomotive at each end of the line.