It's the eggs in pancake batter that hold everything together and provide structure for the little air bubbles that cause the pancakes to rise while they cook. The other thing that eggs do for pancakes is provide richness and flavor, mostly from the fatty yolks. But, just like butter, too much of a good thing is not always a good thing. Too many eggs in pancake batter will make them dense and custardy... more akin to a soufflé than a pancake. Not enough eggs will make the pancakes dry and with a texture that's similar to biscuits. (Which is exactly why we don't put eggs in biscuits.) In this recipe, 4 eggs is the magic number, striking that delicious balance between flavor, structure, and tenderness.