When it comes to relationship, guys and girls work on very different wave length. Most research suggest, that for girls, relatioship is more as an emotional thing, where for man, it is more as a practical thing. And this is biological, not psychological, so it applies to both gay and straight people, a genetically coded personality.
As a result, when it come to determine whether a guy would date a girl, girls become more like the goods/product within the transaction (Sorry, to be so bold, but that is the fact, for guys, when it comes to dating, girls are weighted very much as an object, in determine whether the guy want to get involve with her, sorry.), it is mostly to do with the ide of "by getting into this relationship, what do I get in return." Quiet frequently, good looking, is something that a guy want within the girl they are involve with (At least good looking when they were younger.) But the idea for physical appearance to be the only thing a guy care about is also not true, for example, if the girl is somebody that would sleep with all your friends, most guys will consider her as damage goods for marriage and as a resul, the chances are you won't want to get married to her, at most you want to sleep with her, only. And because, sooner or later, all girls will get old and ugly, in serious relationship, they do consider other attribute, which they believe my be good for them too e.g. is she good to your mother, does she love you, is she good to you, will she be a good mother, is she a gold digger, will she spend your money on expensive shoes and while man of older generation do not want to, most men these days, perfer a girl who have a decent job, this way the family can have two paychecks coming in or the couple can therefore keep the money seperate and only use their own.