In World of WarCraft, Telredor had an elevator that transported them toward the top of the mushroom. However, that would not be an intelligent way to elude orcs (especially since there is a path that leads to the mushroom where Telredor stands). There wouldn't have been a great distance of time between the Rise of the Horde and the First War, so the draenei probably stuck it out until they knew the majority of clans had left for Azeroth. Besides, if mages did exist at that point in time, I'd imagine "Conjure Water" and "Conjure Food" would suffice. xD
And to answer your question, Vel, it was the perfect hiding spot. It was a short distance from Shattrah City and when there was fog, the tops of the mushrooms were hardly visible. Think of it as preservation.