I'm just going off the tech report from the AVSForums. No idea why it would be included and possibly locked out intentionally though. I'd suspect it may simply be some sort of authoring mistake, as this has happened before with high-profile Warner releases (e.g. The Ultimate Superman Collection), and especially considering that the Special Edition DVD of GK includes both audio tracks.
I'll admit, it's a pretty subjective choice of words describing that thread, but statements to the effect of "I wasn't that interested in the English audio", "This went from a possible buy to No way in hell" and "I wasn't going to buy this, just rent. Not that now either", just took me aback. The vast majority of people were indeed being sensible, but for the aforementioned comments, it simply seemed very odd to me that even the presence of the near-universally acclaimed definitive voice of Batman wouldn't be a primary selling point. I guess with Conroy involved, I never considered the potential (non-)inclusion of secondary audio tracks to be a deal-breaker for anyone, especially considering it's unlikely they grew up with the Japanese dub of Batman: TAS. Plus, with the move towards mono-language anime DVD releases, sometimes regardless of whether an English dub already exists, I'd have thought people would have given Batman an easier time. Clearly I'm mistaken, but regardless, it's all a fascinating learning experience to see as to how media content providers are expected to best please most of the audience most of the time.
I wasn't intentionally suggesting anyone actually said that; it's a paraphrase of WW2 propaganda "You have never heard Shakespeare until you have heard him in the original German". It was further appropriated and paraphrased in Star Trek 6 for Klingons, etc. In other words, a slight jest, nothing more.