Why are you restricting it to "large animals"? "Take with you seven of every kind of clean animal, a male and its mate, and two of every kind of unclean animal

Why are you restricting it to "large animals"? "Take with you seven of every kind of clean animal, a male and its mate, and two of every kind of unclean animal, a male and its mate, and also seven of every kind of bird, male and female, to keep their various kinds alive throughout the earth." —Genesis 7:2-3