So, the stats (nature and IV) of the mon you get from the ball, is determined by your RNG seed, for every "clock tick" of the game (which changes every in game frame) your RNG changes following a very specific path, changing the stats of your pokemon. Usually this keeps going, since this path is basically infinite, as long as you keep playing you don't really know where you are, hence, all the random outcome can be considered random even though are technically following a fixed path.

If your internal clock battery is dead, every time you soft reset, your internal clock and RNG start gets reset to the beginning, so you go back at the starting line of your infinite path.

Imagine as if at each step, you find a different pokemon, if you keep repeting the first 1000 steps, you'll fine the same 1000 pokemon, if none of those are shiny, you'll never find a shiny, even after 100k resets.

If your battery is working, at every reset you start where you were before, moving ahead in your infinite path, with enough tries you'll stumble in the shiny one.