Maybe David will implement a method when crafting comes into play, especially if the tower is the only place you can do it.
As far as the game's lore is concerned, it makes sense that Trem's tower is a) hard to find and b)is cut off from the other wizards towers. While alive, he was living in hiding, somewhat exiled from the Wiz guild. The fact the tower teleport can be used one way can be explained as Trem's backdoor, escape route, where only someone whomhas already made it into the tower would be able to use it.