Why are pizzas round when ovens are square and pizza boxes square?

Seems like a waste of available space. If my calculations are correct, a circle shaped area is 78.5% of a square's area, when both share the same width/diameter. There's room for lots of extra ingredients or toppings.

MHO will go out to the most inventive answer. Too serious and you'll get disqualified.

Why are pizzas round when ovens are square and pizza boxes square?
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