Because being able to do easily something that should be able to be easily achieved, as changing your ID/SID without the need to start a new game, and being able to get LOTS of different and incompatible shiny spreads on the same game, is WAY over the line, my friend.
So, because a few butthurt purists frown upon it, you get blacklisted for it? Who cares if you get loads of shinies on one game save? How does that negatively affect anyone? If you trade one of them, the person on the other end of the trade gets a flawless shiny, which is 100% legal. Yay. If you battle with it, its IVs are completely, 100% produced by the game with zero intervention form external devices, so it doesn't affect your opponent in the slightest. The only thing that has been changed is a piece of information which results in the game producing an aesthetic change.
Not to mention the fact that actually getting the shinies still requires a lot of effort and skill.