Because we know how often people pull a 1 in 2,147,483,648 which is the odds of getting 31s in all IVs plus the nature assuming you're using a synchronize Pokemon. BEST CASE SCENARIO.
Oh, it's "probably" hacked. No, if you have 31 IV max legendaries they are hacked, and even if there from this game where it's only 3 variable's I'm inclined not to believe you, but if they are from non-X/Y games you are a hacker or at least have a hacked pokemon.
now they will tell you that rng exists and try to imply that rnging isnt the same as hacking
And as if most people that havce 6IV pokemon actually have the patience to wait hours or days for the perfect moment to start their encounter to get the shiny 6IV Legendary pokemon that they so desperately need (and that's not even counting the time it takes if you've messed up and need to restart the encounter).