Men keep their real personal feelings hidden for the same reason women keep their real faces hidden (with makeup). Both men and women fear rejection from the other sex and from society at large. Men want attractive women, so women hide their physical flaws. Women want strong providers, so men hide their "weak" feelings. 
See “A Comprehensive Look at Gender Equality: The Doctrinaire Institute for Women's Policy Research” www.malemattersusa.wordpress.com/2012/02/16/the-doctrinaire-institute-for-womens-policy-research/