There are several reasons why round pizza is easier to make than square pizza, and these reasons can be applied to other situations too.
As you might have guessed, the first reason is that it is easier to cut around pizza slices because you can easily get a slice that is not too thin.
This makes round pizza slices easier to eat than square pizza slices because more of the toppings cover the slice of the pizza.
Also, because of the shape, the round pizza slices hold more toppings, which are put on the round slices more easily because there are more flat sides to place your toppings on.
However, there is the basic theory behind why round pizza is easier to make is that you can get the whole dough to fit into the pan.
If you have a flat crust, it must get rounded over the pan to cover the sides. If you have a round pizza, it can just drop right into the pan and cover the sides.