Answer: Most likely, batting average calculates the number of hits or home runs per times at bat, and does not account for walks and sacrifices.
Explanation: A batter who gets a lot of walks (base on balls) has a lower average than a hitter who gets a lot of singles. And that does not account or the batter's important skill to distinguish between a good pitch worth taking a swing and a pitch that's out of the strike zone. He gets on base and avoids an out.
A sacrifice (often a bunt) to advance another runner counts against the batting average, and may lower a player's "value" in the minds of those who look only at the batting average. Yet, the sacrifice was probably called for by the manager in order to improve the chances of having a player score a run.