There are two main points, why camps and castles are not buildable in the war of the ring.
First of all, on every map there can only be a limited amount of camps and castles, so if you are playing on a 2 player map in WotR, there will be only the 2 camps/ castles. But if you play with more than two players, everyone but two of them would not get any camp or castle, so they will be much weaker, or even absolutly useless. Also the starting position in the WotR depends on the territory you came from. Therefore it might happen that you will have no chance to be at the camp/ castle before your enemy is there, or if your enemy has cavalry. These things would destroy the whole WotR mode.
Instead, our plan is that all camps and castles on the map are replaced by outposts, so in addition to the normal outposts nearly every player can get one at the start of the game, and an outpost is not that strong that a player without one has no chance at all.
The second point is the whole concept of WotR. When you play on the livingworld map and fight a battle you have to options, either to auto-calcuate the battle by the computer, or to fight the battle by yourself in real time. This real time battle is supposed to be the exactly same battle, with the slight difference that you can act much more intelligent and use different tactics with your army, instead of clashing them on each other. But what the real time battle really was, was just a normal build up game. You play a battle you would have lost for sure, because you had hardly any units in the land, but you build yourself up until you have an army with maximum strength, so after finishing the battle the whole army will be transferred into the living world, where it is that strong that every other fight is one.
But that is absolutly contradicting the idea of WotR. Instead of making tactical decisions and conquering enemy lands, you fight on battle and overroll your enemy afterwards. If one battle decides the rest of WotR, you can also play a normal skirmish.