Here's my theory.....
The crowd at MK follows the "right hand" theory which states that the majority of people are right handed which means they will naturally tend to go right at the castle to Tomorrowland. They spend the morning at Tomorrowland and when its time for lunch they eat at Cosmic Rays. This is why Cosmic Rays is the world's busiest fast food restaurant (see you learned something today).
My family and I tend to go left or straight at the castle for this reason. You can visit the attractions in fantasyland or adventureland without a huge wait and we like to have lunch in liberty square.
DWD