Passive men and plain women aren't sexy!
Certain ideals are expected to be embodied by male and female characters for them to be seen as attractive to the opposite sex. Sexy female characters are physically desirable; Sexy male characters are strong and proactive. This is a consequence of Men Act, Women Are as applied to sex appeal: A woman's attractiveness is mostly due to her passive physical attributes, while a man's attractiveness is mostly a result of his behavior. For female characters, passivity does not detract from their attractiveness. In extreme cases, female characters who are very active will be seen as undesirable, or that they can only love a man stronger than themselves. Further a physically unattractive woman will always be unattractive regardless of how proactive she is. Male characters are viewed as less attractive if they are passive. In fact a dynamic evil man is more likely to be viewed as attractive then a decent but weak man. A physically unattractive man's dynamic qualities can also make him more attractive. Some male characters who are physically attractive-particularly in a "pretty boy" kind of way- will be seen as weak, less than a man, or suspected of being gay. This holds doubly true if they spend time cultivating their attractiveness. (In fact, many male characters with a large female following tend to be disliked by male audience members- possibly because he's a threat to their sense of masculinity.) In summary, physical attractiveness only ever adds to a woman's sex appeal while being active may or may not detract. Whereas for men being proactive only ever adds to a man's sex appeal while being physically attractive may or may not add to his desirability. These differing standards lead to the genders being held to equally damaging but different standards of attractiveness and have numerous Unfortunate Implications. For women the implication is that your actions are irrelevant to your attractiveness to the opposite sex. As long as you're beautiful, even if you're 105 lbs of useless deadweight or utterly psychotic you're still desirable. The Unfortunate Implications for men is that men are shallow and only after one thing, thus they don't care if a woman is a dynamic, active character. Also, male characters will end up pulling more then their own weight, emotionally and physically, in works where this trope is in effect. And, just like the beauty ideal puts incredible pressure on women to be beautiful, the strength ideal puts incredible pressure on men to judge themselves against an impossible standard of stoicism, willpower and physical strength. These pressures have not received as much press or attention on their effects on men and boys, partially due to the idea that men aren't as emotionally fragile as women, that things that affect women are worse than things that affect men. This in turn enforces another Double Standard: That women must be defended from the evil media, while men should be able to just shrug it off. In the last few decades there has been more of a push to create attractive, dynamic female characters. Unfortunately this often seems to come at the expense of the male characters they are paired with who are portrayed as incompetent and emasculated. It is a hard balance to strike, and difficult to imagine a work in which a beautiful, virgin male character is saved from peril by a grizzled female Anti-Hero who is changed for the better by his pure heart, without the man seeming like a useless wussy-pants whose wuss-ness disqualifies him from being a man and, more importantly, from being saved. This is the supertrope for Ugly Guy, Hot Wife, Beast and Beauty, Cookie Cutter Cuties, Hollywood Homely, Non-Action Guy. See also Beauty Is Never Tarnished, and the unequal application of Dirt Forcefield.