Go figure :/ There were plenty of assets to use from Donkey Kong Country Returns and Metroid Prime Hunters ://If it is the Magicant: why make a new Mother stage, but not a new DK or Metroid stage?
I know no one can really answer that, but I don't see the logic in making a new stage for a rather small series, and reducing DK and Metroid to just one returning stage.
Same goes to Sonic I guess, with Sonic Rush, Rush Adventure, Generations and Lost World on the DS/3DS, there is no reason to bring freaking GHZ back.