Why do they have an HD transfer of the old theatrical cut if they don't have one of the more recent and far higher-profile reconstruction?
I'd imagine that scanning film elements for the theatrical cut is rather straightforward and a cost that can be easily anticipated. If the Extended Cut was indeed finished on tape 10 years ago they'd have to completely reconstruct the film, scanning the raw elements before editing them together, which is an entirely different process, and FAR more expensive. As we've seen, the studios (and the media empires that own them) may have a lot of money, but what they give specific projects on a budget is usually relatively little, and is not forward-thinking.
So, in 2003 or so Warner saved money in the moment and compiled the Extended Cut in SD. And now apparently they don't care to budget doing it all over again - which from a cold business person perspective one can understand as the film will most assuredly sell less than 5000 copies, and an immediate return on that investment is not going to occur.
This particular film is suffering for the era in which it had the budget given to it to be reconstructed into its Extended Cut. It's not alone in this. Hell, if Paramount wasn't willing to put the money up again for the cash cow that is Star Trek, is it really that much of a surprise that Warner would pass on throwing more money at The Big Red One? (And you have all the right to say the same for the final product they are marketing).