I thinks it got to do with being comfortable and being willing to experiment. Ive kissed a few of my girlfriends. At first it was for pure curiosity, and feeling what it would be like to kiss a girl and if i found it arousing in anyway.
Well, good news for my BF.. i didnt find it arousing, But i found it soooo much fun!! Woman have the BEST lips! soo soft.. and they kiss better than a guy does, Nice and gentle. Woman understand eachother and know the way they want to be touched.
So yeah, id say curiosity and purely for the fun!

... NOT because they CANT get a man!, If anything, theyd be able to attract more men because most guys LOVE seeing girls "Hook up".