It took me a while to realise this, but post-production doesn't just include computing power, it also needs people.
In a traditional film, "post production" starts after the actors have filmed their bits (principal shooting). Editing, music, CGI, voice recording, etc. are all part of it. Basically, putting together the entire film.
In animated/digital works it is much the same. All the background, dialogue synching, music and final rendering are all part of post-production.
It wouldn't surprise me if they just ran out of money or funding.
