I think Sony has the distribution rights for the movie in the US but Metrodome has the original transfers and source material. The Sony DVD transfer is different from the HD transfer used on the UK and Australian Blu-rays. Maybe Sony has been unable to reach an agreement necessary to acquire the HD transfer or maybe they are just waiting a couple more years so they can release it as a "30th anniversary edition".

Sunbow is now owned by TV Loonland, so Sony would probably have to license the title from them.