Pokémon Logic:
> Create a Legendary
> Create a Shiny Form of said Legendary
> Now code it so it's impossible to be shiny.
Completely logical.
http://www.serebii.net/games/shiny.shtml
[
I know at least one of you will say "there's always events - they can be shiny then."
Yeah, no. They never do that. Each shiny Legendary they've released can be obtained without events, so... yeah. The "event" thing means nothing. ]