rh310
Hall of Fame
Because it is, that's why! That's also why almost no top pros do it.
Besides, how will you ever learn to hit decent volleys if you're so used to using only one face of your racquet by flipping the racquet upside down?
Let me make sure I understand your question: How will you ever learn to hit decent volleys if you hit "rally" groundstrokes without changing grips?
I'd guess you'd learn to hit them the same way if you hit rally groundstrokes with a change of grip:
You'd practice them.