first of nice taking my post out of context for those that dont want to look up vlad brought up tmorph as look tmorph is banned. which Is ban becasuse it goes in and starts modifying core game files. it you can play as a orc but make your character look like human. is a .exe file that is is actively injected into wow. which is something that blizz can detect as this thing actively modify the game.
addons on the other hand are passive they sit between the player and the game and only work with the approved files when they come up they dont even override the file they just filter it to the player. to give and example take a glass of water put a blue lens over it thats an addon and. tmorph on the other hand is taking the water and dropping blue dye INTO the water. blizz cant tell what you put in the water but they can clearly tell the water is no longer clear.