In all their infinite wisdom, Nintendo released every single Metroid Prime game in the shadow of the Halo releases.
Obviously Metroid Prime is nothing like Halo, other than being a science fiction themed first-person shooter. And I know there's going to be someone who leaps on this to honk at me that Metroid Prime is "an adventure, not a shooter", so let's just get the semantics right out of the way. It has a first-person perspective, and you shoot aliens. To a casual player who doesn't follow the press and doesn't know the details of what Metroid is, they look close enough, and Halo has the power of name recognition where Metroid Prime does not.
If it had only happened once, it could be forgiven as a strategic mistake. They thought that the success of Halo would get people excited for sci-fi shooters, and that they could tap into the new market for console FPS games that Halo would create. This did not work. If they had changed tactics and learned from that mistake (Nintendo learning from a mistake, heaven forbid) it would just be a single misstep. But instead, they did it for both of the sequels (Hunters being the only exception). Now, as a result of the poor sales this has caused, the board of directors has been made skittish, and that's why Nintendo does not do any in-house or second party (like Retro Studios) Metroid games any more.