Problem with bull rush is the need for a charge, plus being unable to adjust the trajectory of the push. If you wanted to lob someone over a wall or move them back or sideways you're just out of luck. Meanwhile with reposition, you have to move an enemy into an unoccupied space that they can stand in, in addition to the minimal range.
I think the part of the problem is that if there was an ability to throw people, it would completely invalidate bullrushing, so perhaps that's why there's a lack of rules regarding this.
