Kirby has an entire company backing him up.
Ever since Iwata shuffled Nintendo's internal development teams back in 2005, Metroid hasn't really had a consistent team to keep making games for it. There was Retro, but they moved on to Donkey Kong Country. It's somewhat telling that Sakamoto seems to keep having to bring in outside studios like Team Ninja or MercurySteam to assist developing his new Metroid games.
Who knows whats going on with MP4's developer. I'd assume it's just a new internal team they brought together to make it, but a lot of people like Shikamaru Ninja seem to think it's Next Level Games...