I'm not sure I'd want to sell those kit if I was the Pyra seller. From what I've heard the case need modifications, like sanding at places or cutting something or whatever.
So it's not just a kit that people can mount. If people mount them without altering the case, some issues may arise, and complicate post-purchase service.
If they would sell the kits with the modifications already made, them the time to prepare the kits would be close to the time to prepare a fully built Pyra, so little point.
I don't know. Maybe it depends on the user skills, but it would also require more extensive mechanical documentation...