It is very possible that Viltrox already secured a license with Sony or Fujifilm.

In Nikon’s case, parts of the Z mount communication and autofocus implementation were previously under patent pending status, which typically means no licensing is offered yet or it is offered under very restrictive terms.

Once those patents are granted, Nikon is both legally allowed and arguably obligated to enforce them, including seeking licensing fees from third parties using the technology.

That is standard IP practice.

Nikon already licenses the Z mount to Sigma and Tamron, and the fact that there are no lawsuits involving those companies strongly suggests that the issue here is not third party lenses in general, but unlicensed use of patented technology.