When they increase the size of the cylinders in engines to get more displacement in the same basic block, the cylinder walls get too close together. That means there is no good path for coolant to get between the cylinders, so small vent holes, or steam holes, are put in to allow coolant in the area.
Most older engines just relied on coolant to flow through the block, to a passage in the deck at the back, up into the head, and back to the pump. Eventually they figured out that additional coolant holes along the way helped cool cylinder walls and hot spots in the head as well. Even in the 80's they still were not doing them right.
