I don't understand how this question falls outside the scope of Christianity.SE:
There were related questions on BH.SE here and here.
A logical answer to the OP from my perspective would be that the NWT translators made translation choices in the light of JW doctrine. Whether these choices are defensible from an impartial (is there such a thing?) perspective or not is relevant to BH, but the motivation for the choices and how JWs defend them is surely on-topic isn't it?