A few theories -
-Nintendo are perfectionists with their content. Either they wanted more revisions on principle, or some of their recent brand empowerment (this year was wonderful for the company) has given them more leverage OR reasons to go back to the drawing board.
-UC or someone got cold feet with D23. I don't want to accuse the company who've actually done things the past decade of being caught with their pants down, but I truly think they were caught off guard somewhat. There has been a rapid reshuffling of projects and priorities with - for whatever reason - Nintendo getting caught up in it.
-Classic reason Star Wars was held up, the board sent them back for improvements. They want more.
-Osaka could be as simple as contractor issues, but I doubt the olympics are effecting them that gravely in the South. Plus OLC is making good headway. I think the fact Osaka is also a bit held up gives more credence to late changes.