What blows in particular is that some of those games only found their way stateside via the Wii store. Sin & Punishment comes to mind. You can find ROMs of the original Japanese N64 version online, but I doubt anyone has ROMs of the US/PAL versions for the Wii that had localized menus (the dialogue was already in English).
Given that the Wii Virtual Console games were a bundled emulator and ROM, and you could swap the latter out, I imagine the content is indeed available.
I can't really speak for the main reason why, but my guess is that it gave Nintendo a level of flexibility with localizing the game without having to set up a Nintendo 64 development environment.
In all seriousness, that tracker is not the only tracker that has the data. There are many public trackers carrying all of the eShop games for the Wii, and these full sets have the game. All of these dumps cataloged in the No-Intro DAT collections, so you can verify that you have a set of known good dumps.