I think it has to do with this:
What is the meaning of the name Jehovah? In Hebrew, the name Jehovah comes from a verb that means “to become,” and a number of scholars feel that it reflects the causative form of that Hebrew verb. Thus, the understanding of the New World Bible Translation Committee is that God’s name means “He Causes to Become.” Scholars hold varying views, so we cannot be dogmatic about this meaning. However, this definition well fits Jehovah’s role as the Creator of all things and the Fulfiller of his purpose. He not only caused the physical universe and intelligent beings to exist, but as events unfold, he continues to cause his will and purpose to be realized.
Therefore, the meaning of the name Jehovah is not limited to the related verb found at Exodus 3:14, which reads: “I Will Become What I Choose to Become” or, “I Will Prove to Be What I Will Prove to Be.” In the strictest sense, those words do not fully define God’s name. Rather, they reveal an aspect of God’s personality, showing that he becomes what is needed in each circumstance to fulfill his purpose. So while the name Jehovah may include this idea, it is not limited to what he himself chooses to become. It also includes what he causes to happen with regard to his creation and the accomplishment of his purpose.
From the appendix of the new Bible (http://www.jw.org/en/publications/bible/nwt/appendix-a/tetragrammaton-divine-name/)