Larger Players . Athletes in all sports are getting larger, but baseball is different in that increased strength and power favors the hitter. Yes, more pitchers throw in the high-90s these days and strikeouts are more prevalent. But arm mechanics and physical limitations of the elbow and shoulder joints pretty much precludes that we will ever have a 110 MPH pitcher without. Hitters do not face these potential injuries, allowing the ball to be hit harder and further.
Hitters work out with weights nearly year-round.
Decreased Premium on Defensive Skill . Throughout baseball history, the importance of tangible defense skills has continually decreased. Gloves are bigger, fields are perfect, balls are perfect. Defense is easier to play, and therefore there is a less of a premium on defensive skill. Even at the skill positions, managers have more freedom.