In baseball, pitchers tend not to be good hitters.
In the American League, they have a designated hitter.
Instead of the pitcher batting, they have someone else bat for him.
Players who don’t field well often are designated hitters.
In the National League, they make pitchers bat.
Or a pinch hitter bats for them, and then another pitcher has to take over pitching for them.
Major League Baseball saw that pitchers were an easy out or would bunt a runner along the bases.
So, they decided to relieve all pitchers of hitting duty.
By locking all of the players out.