Given that novelWriter itself is GPL licensed, I doubt this is the problem. More likely it was a choice to avoid needing pandoc as a dependency, either explicitly (bundled or integrated in the code somehow) or implicitly (calling to the system's pandoc install), as pandoc is written in Haskell and kind of a PITA to build or integrate in that way.

Since you can already export to a single ODT/PDF/MD, the benefits of additional pandoc integration are probably diminished.