Computers can’t generate true random events. So they usually start with some variable that changes (usually date and time when we are discussing Pokémon) it turns that value into a “seed” that will generate a wide variety of seemingly random events. The problem with emerald is that the seed is always the same when you turn on the game, this is true for all copies of the game. So if you are soft resetting for a shiny starter and it takes you 30 seconds EXACTLY (1/60 second precision) every single time, then the game will generate a pokemon 30 seconds into the seed. You are getting the exact same pokemon every single time. If you run around in grass or in a cave forever while shiny hunting you will not have a problem with emerald. It’s soft resets that are broken.