1 A sign of high estrogen
Big eyes along with full lips are signs of high estrogen in women. Men are hard wired to find women with higher level of estrogen more attractive.
2 They make women look younger
Larger eyes make women look younger. Men in general prefer younger women to older ones.
3 A sign of fertility
Because Youth is considered a good sign of fertility men usually find women who look younger more attractive as men are hard wired to get attracted to fertile women. See also what makes a woman attractive to a man.
4 Connected to innocence
Since babies have large eyes people have learned to associate some traits such as honesty and innocence with large eyes.
5 A sign of femininity
Testosterone makes a person's eyes small. A woman who has large eyes is perceived to be more feminine. See also how to tell if a man has high testosterone.
6 They signal the need for protection
Women with bigger eyes make men unconsciously believe that they need protection since they resemble babies. This makes those women more attractive to men.
7 They make a woman look agreeable
Large eyes can make women look agreeable and submissive. Many men like to see those traits in women.