It appears that Metroid Prime Trilogy has been discontinued - at least in the USA according to a post from Coffeewithgames
. We have contacted Nintendo in the UK for local comment.
The post includes a response from NOA regarding the unavailability of the title, "Thanks for your e-mail. The earlier response regarding Metroid Prime Trilogy was correct: it is no longer being shipped. When first introduced, it was announced that there would be limited availability. However, a reason for this was not announced. That being said, you may still be able to locate a copy via stores that specialize in previously played or used games."
Can't be any more cut or dried about it. Read this
to see what you're missing.