Why is there no Tamron 17-70 f/2.8 for Nikon Z?
Tamron has been allowed to make first-party lenses with Nikon blessings for a long time. And, if you look at their offerings, most of them are for full frame. The excellent 28-75 f/2.8 G2, the 70-180 f/2.8 - both of which are a fraction of the price of the similar Nikon counterparts, and thereby do cut into Nikon sales.
So, why isn't there the Tamron 17-70 f/2.8 - which is widely said to be among the best lenses for Sony APSC? It even has VC, which would help a ton since no Nikon DX body has IBIS. The only option there is the Nikon 16-50 f/2.8, which is twice as price and has a shorter long end.
Bringing the 17-70 f/2.8 would, I believe, improve both Tamron and Nikon sales since Nikon does not have third party fast aperture zooms (even Canon has 2 Sigma RF-S lenses!!!).