AFAIK it all boils down to the fact that during embryonal development our cells, which at that point were just a blob of undifferentiated autonomous chemical machines, somehow managed to unanimously agree upon the cardinal directions (up-down, left-right, front-back) for future development - and thanks to this, we don’t have toes growing out of our ears.
It’s not that incredible, considering we can get cysts full of teeth and hair inside the body
Imagine if you suddenly sprouted a tumor with functional tastebuds in your colon