You don't have to go far to see proof of this. Many straight women I know, although they will be sexually attracted to men, say that women have more "aesthetically attractive" bodies. Most women I know spend as much time checking out women as they do men. Women's clothes are designed to reveal the body(think yoga pants, cleavage, etc.) while men's clothes are designed to cover it up as much as possible(think suits). Boobs and butts, traits that every woman possesses, are things that have been sexually glorified. However, there are no traits on a man that have been sexually glorified. Penises are considered ugly by a large part of society. Even the traits that are considered "attractive" on male bodies(such as muscles) are things that primarily exist as function and are not considered inherently beautiful like curves on a woman. Art mainly features women and not men. Not to mention, improving your appearance is considered feminine and not masculine.

The honest truth is no one knows what is sexually attractive on a male body whereas everyone knows what is sexually attractive on a female body. Everyone knows that boobs, butts, and legs are sexually attractive on a female body. However, no one really knows what is sexually attractive on a male body. Too many muscles and you are unattractive. Too few muscles and you are unattractive. Abs are considered too much for some women and are attractive to other women. The only real constant is height, and that isn't necessarily sexually attractive(women don't suddenly become distracted whenever a tall man passes by them). Now, an observer might chalk it up to women having different "types" and this is true. However, the reason for these types is that male bodies are inherently considered less sexually attractive and therefore, no woman has a baseline idea of what is sexually attractive on a male body(this is in contrast to female bodies, where boobs and butts = attractive have been nailed down on us from day 1).

Ancient Greece/Rome considered male bodies to be just as attractive, if not more attractive than female bodies. Married women were literally not allowed in the Olympics due to the belief that they would go insane with lust upon seeing the young beautiful men. However, things have changed and in our society, female bodies are the gold standard for attraction.