With the left hand shielding the liver side, the right hand becomes the weapon bearer.
With the left side protexted, the deaths by liver puncture is greatly diminished.
This is called survivorship bias.
> The stair spirals counter-clockwise and is known as the "left-handed staircase" as it would put right-handed attackers at a disadvantage. The story is that in 1513 when the left-handed Sir Andrew Kerr came back from the Battle of Flodden, he had his men learn to use their left hands when swordfighting. In Scotland, left-handedness has been dubbed "Corrie-fisted" or "Kerr-handed".
What you describe is a selection pressure for right-handedness.