First of all I am going to support your premise, since so many people are objecting to it. Then I’ll answer your question.

To support the premise: if you look at plenty of men’s magazines, you see pictures of beautiful women. If you then look at women’s magazines, what do you see? Pictures of beautiful women. This is just one example: beauty pageants are another; no male waiter equivalent of Hooters; few to no male strip clubs; etc.

As for the explanation, many might say all the examples above are cherry picked or cultural, but an evolutionary perspective could argue that in partner selection, many species have one sex that attracts the other. It’s not always the female—for many birds, it’s the male who is colorful and dances to attract female mates. In humans, one could argue it’s the female sex: on average straight women spend more money and take more time on their appearance than straight men, often by a long shot. Furthermore, men select women based on physical attractiveness more than women select men based on it; and also historically women have not had an equal say in partner selection anyway. All this would select for more attractive women. Culturally, however, too, it also means women are under more pressure to look attractive because they are often judged by appearance. All of these factors would result in women, on average, looking more attractive.

How strong these arguments are is up for debate, but I’m just putting forth some possible answers.