The reason I don't think it made sense is because the value of the acquisition depended on integrating Weta into the Unity software. They marketed it as: "use all of Weta's tooling in Unity".
2 years later and that never happened. I would guess that's because it's quite difficult to jam a software platform into another software platform.
Unity has a long history:
> 1) acquire some software/tech
> 2) attempt to integrate (force) it into Unity
> 3) fail
> 4) scrap the integration
Based on what I've heard about how Unity operated under John R, this was likely a scenario where the head honchos recognized a business synergy and didn't consult the engineers on how feasible integration would be.