>>16263112First you determine which stats will be inherited in the bred pokemon (which is where the 1/6 chance comes in). These states will not change if you soft reset to before the egg comes, so you go back and replace the parents of that egg with pokes who have 31s in the IVs that *will* be inherited.
This is better because you can easily determine which stats will be inherited from which parent, which reduces the number down to 1/6, assuming you don't care about the stat that won't be inherited.
tl;dr: rng abuse
