A note on why people tend to sleep on the right.

People likely sleep on the side that causes least muscular tension in their body.

People tend to have a pelvis that is turned slightly to the left (something referred to as the "left aic, right bc pattern") this due to a combination of factors stemming from internal asymmetry, like the liver giving support to the diaphragm on one side, which effects how we use our muscles to breathe. With time many of our movement patterns become slightly asymmetric to make breathing more efficient.

This asymmetry is likely the main contributing factor in the dominance of right side sleeping.