You've specifically asked 'Why'. The NWT translation was made about a century ago if not more. Assume the reason is love. Its probably the real reason, knowing what JW's are like. If want a technical answer its probably too late. The language has been drifting for a century, and the 'NWT' is no longer new. Another possible reason is that somebody wanted to screw over the JW's. That's possible, too.KJV
17 Therefore doth my Father love me, because I lay down my life, that I might take it again.
18 No man taketh it from me, but I lay it down of myself. I have power to lay it down, and I have power to take it again. This commandment have I received of my Father.
JW
17 This is why the Father loves me, because I surrender my life, so that I may receive it again.
18No man takes it away from me, but I surrender it of my own initiative. I have authority to surrender it, and I have authority to receive it again. This commandment I received from my Father.”
If you read verses 17 and 18 in the kjv.And the jw one.The wording is not the same.I like how they handled it better in the kjv.
I got the bible verses comparison from post 4.
King James reason was not love. His reason was perhaps a mixture of love and practicality 5%/95%. He needed to divorce his wife, but the clerics did not themselves comprehend his need. Clerics were men without wives or at least not with publicly acknowledged ones. James was in a difficult situation. This, among other motivations, led him to authorize a translation of the canon. It was less of an effort to produce the most explicitly helpful translation as it was an effort to get him free of the power of the clerical dynasty. He did free himself. He did start a new and more free fork of the Roman Catholic faith. As an intellectual he probably was hoping to help his people, his Britain; but that is only a guess by me. His overriding reason seems to be that he wanted to obtain a divorce.