Men, Women, & Being Professionalism at Work?

Why is it that older married men at work like to flirt with young women, call them "pet names" & check them out? I think it's very unprofessional, esp. if the woman is not coaxing/encouraging him or wearing revealing clothes. I'm a shy kind of girl & one of my officemates is constantly doing this. I've heard it's only me that he does this to. He also asks my opinion on certain things. A lady coworker of mine said it's because there is no respect/validation at home/from the wife. Why do they fixate themselves on one woman & not do this to other women in the office?