The existence of the NCAA doesn't have anything to do with it. It is, however, somewhat of an accident of history that the MLB draft is of high schoolers as opp

The existence of the NCAA doesn't have anything to do with it. It is, however, somewhat of an accident of history that the MLB draft is of high schoolers as opposed to AA/AAA players. Before Branch Rickey pioneered the concept of "farm systems" in the late 1930s, a quarter century after the NCAA was established and around 75 years after the first collegiate baseball game, minor league teams weren't affiliated with MLB teams at all; instead, they were just other leagues with younger/worse players whose rights would be available to the highest bidder. The MLB draft to distribute talent didn't start until 1965, by which time all the teams had well-established farm systems via affiliations with minor league teams. The unpredictability of the gap in performance between high school and pro, though, is IMO larger than in football or basketball due to the fact that the core talents for making it in MLB are not based on pure run-fast-jump-high easy-to-measure athleticism, but rather on reactive skills that even if present in high school are not observable against meaningful competition.