President of Retro, Michael Kelbaugh, stated that one day his studio might consider producing another Metroid game; however, they chose this year to go with Donkey Kong. The newest version of Donkey Kong subtitled Tropical Freeze was unveiled for the first time at the 2013 E3 conference.
Kelbaugh explained that the company felt that they had unfinished business that they could still turn into a Donkey Kong game and that they wanted to focus on that because there was no way that they had the bandwidth in order to work on two major gaming titles at the same time.
In an interview that Kelbaugh gave with IGN he carefully picked his words so as not to appear to favour one game over the other. Instead, he simply explained that when they completed DK they still had some great ideas for where they could move forward and given the great manoeuvrability of the Wii U they felt that it was the time to continue with DK.
He reiterated that Retro Studios loves Metroid and that they have every intention of one day working on creating another Metroid but for the time being they have had a great time working on creating a new DK game.
The retro Metroid game is pretty much a cult favorite with many hardcore gamers in love with the simple screens of the original game. However, the numbers speak for themselves as Metroid 3 sold 500,000 copies while Donkey Kong Country Returns was able to sell a whopping five million copies.
Therefore, if Retro was only going to bring back one retro gaming title for the Nintendo Wii, it is pretty clear why they made the choice they did because the potential gaming market and client base or Donkey Kong remains much larger.