Conservation (or lack of) angular momentum.......
In the book on Hitting Biomechanics they discuss the barrel losing velocity/acceleration when the hands get away from the body. They have thousands of analysis to support their research. I like Ted Williams thoughts on this in his video as well as Ortiz, about keeping the hands closer to the body. Ted also said it's a shorter swing and it's "tougher" to get the swing going with the hands/barrel away from the body.