One reason outfielders don't have stronger arms might be they don't practice as much as we did. Most teams today don't take outfield practice. Another reason is baseball has to compete with other sports now - basketball, football, soccer - for the better athletes that might have more skills and stronger arms.
For all the time schools devote to the teaching of mathematics, very little (if any) is spent trying to convey just what the subject is about. Instead, the focus is on learning and applying various procedures to solve math problems. That's a bit like explaining soccer by saying it is executing a series of maneuvers to get the ball into the goal. Both accurately describe various key features, but they miss the what and the why of the big picture.