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Why did DIPS theory describe many balls in play as luck from a pitcher’s perspective?

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Green retro manual baseball scoreboard beyond an empty, neatly mowed baseball field with brown infield dirt and striped grass outfield. — Sabermetrics A scoreboard provides some – but not necessarily the most useful – data on player and team performances in baseball.

Defense Independent Pitching Statistics (DIPS) theory, developed by Voros McCracken, posits that a pitcher has limited influence over the outcome of a ball once it is hit into the field of play.1

According to this theory, while pitchers exert significant control over events they directly influence—specifically strikeouts, walks, and home runs—the results of other batted balls are largely independent of the pitcher's skill. From a pitcher's perspective, whether a ball in play becomes a hit or an out is primarily attributed to luck or factors outside their control, such as defensive positioning and the inherent randomness of batted ball outcomes.12

This perspective is supported by the observation that major-league pitchers show little variance in their ability to prevent batted balls from becoming hits, and that the league-wide BABIP (batting average on balls in play) tends to remain remarkably consistent over time.21