I obviously don't have a clue as to what's really the case, just theorizing as to why left-back might be his preferred position.
Maybe this lad is just bad at crossing and better at cutting inside? If his crosses aren't that accurate anyway there wouldn't be much of an advantage to having him on the right hugging the touchline.
Lee Young-Pyo was one of the best players to ever play for South Korea, and he was a right-footed left-back that was terrible at right-back. He had the same problem: great running with the ball at his feet but not much crossing ability.