Most likely the latter in my humble opinion.
Bear in mind that TFT released a year after Reign of Chaos, and I don't think they began working on it before the release of RoC (at least much before the release).
TFT already added hundreds of new stuff, including dozens upon dozens of model, so I think they didn't have much time to create a specific model for a specific character that literally appears in the campaign and then dies 3 minutes later (who's just a creep, not even a hero).