Well, there is a reason for that.
Basically when you do a normal timetable flight, you have a scope of possible flights to do from where the airplane is stationed.
When you are flying a Tour, normally you don't have because tours are special routes that you do. We don't have flights departing from Alexandria, for instance, so, we would have many stuck airplanes, not to count that if you crash one, you should start the route again so you can continue from the crashing point ...
So, maybe one day we can consider it with a possible reason that could support the PP, but for now, we don't have it.
Regards.