This diagram is a simpler illustration of the water table that forms against your foundation after a heavy rain, or when your home is located along the path of traveling above- or below-ground
water sources. The below diagram shows the resulting hydrostatic pressure that forms in greater detail.
The reason why it’s confined to the area as depicted goes back to when your home was built. The original dig and backfill that followed has less integrity than the surrounding undisturbed land.