With the ratio of symbol drops in skirmishes and even new BG, there would be not enough symbols for people before new raid release. In consequnece a lot of people would be not raid-ready with their toons.
In RoI we had Draigoch that was available to farm not long ago from the release of RoI and gave one symbol just for the completion of t2 and granted 1 to 3 symbols every run (in addition to scales and other stuff). So a lot of people were ready for ToO when it launched or not long time later.
In RoR we didn't have such an opportunity and I suppose Turbine made it that way to make up for it...
Warden(85), Minstrel(85), Rune-Keeper(85), Burglar(85), Captain(85), Hunter(85)