Nikon has one objective, short & long term profitability. Ooops, that's two.
1)They need to be competitive. If someone is looking at a first time or new line of cameras, Nikon needs to fill most of the holes where competitors have offerings, or provide alternative ways to accomplish the same thing. (Is there really a need for 36mp? Perhaps, only for marketing reasons.) Understand that Nikon is not only competing with other major camera makers, but also third party lens makers as well. (Wonder what would happen if Canon came out with Nikon mounts for their lenses or vice versa? Nah… Why make it easier to stick with competitor’s cameras?)
2)They want to feed baby steps to current customers to make it easier to fulfill NAS, and line Nikon’s pockets.
3)One of the roadblocks of evolving DX users to the more expensive FX cameras is the expense of glass. It is possible that this lens could be the 1st meaningful FX glass for current DX users. Even more f/4 glass could then make it easier to “upgrade” to FX when NAS overcomes good judgment. You don’t think that Nikon cares if you buy more stuff than you really need, or causes problems in marriages, paying mortgages, etc., do you?