Why Is "Expanding the Pie" an Effective Way of Negotiating

Why is "expanding the pie" an effective way of negotiating collaboratively?

A) It threatens both parties into giving up their piece of the pie.
B) Someone is always "hungrier."
C) It attempts to expand scarce resources available by altering the conflict structure.
D) People become more entrenched in their "positions."
E) The playing field is "leveled."