I have heard that Nikon was unable to sell the vertical grips it had produced for cameras like the D750, and ended up having to dump them in sales and whatnot. Looking at the extremely low prices new ones sell for on ebay, it makes sense. Of course, had Nikon's vertical grip price not been ridiculous, they would have sold some. The truth is, due to their high price, most people simply went for 3rd party. So from Nikon's point of view, why bother making vertical grips for mid-range bodies, when mid-range buyers demonstrably don't want to pony up for the vertical grip prices Nikon clearly deems fit.
Nikon is also stripping controls features from new bodies, as evidenced by the lack of drive and exposure mode buttons on the Z6/Z7. Likely to help the second gen mirrorless stand out. While many balk at the idea Nikon would do this, I suspect Nikon is aware that shrinking R&D funding and technological advance slowing means future camera releases will be far more incremental than we have been used to in the past. In light of that, stripping features and slowly reintroducing them is a way to encourage purchases of new models. 'Sure, the Z6 2.0 is still 24mp, but now it has a drive/exposure mode buttons and the Z7 2.0 also has vertical grip!'. You can expect to to see things like these along with double exposure, unlocked DX focal lengths, etc. slowly make their way back onto Z bodies if I am correct.