Lets be real, women are a lot more aesthetically pleasing compared to men... I think even straight women realize that when they look at art and look at how elegant and flowing the female form is compared to the rigid stiff male figure with our harsh angles and so on, which I imagine isn't the easiest thing to transfer accurately on media. That's a small point though since I doubt that's actually stopping them in this day and age.
'Women's bodies are innately more aesthetically appealing' is straight-up a cultural/social construct, though. It is in no way any kind of objective truth or fact. It has not even been universally true in all cultures throughout history. I hate to trot out the Ancient Greeks again because they get used as an example for everything, but they absolutely had at least as much of a respect/love/admiration for the male form as the female form, and it shows in their artwork and statuary.
It's a belief that feeds on itself. People believe women's bodies are more attractive/better suited to appealing to their audience -> women's bodies are used as decoration/sex appeal more often than men's -> people are accustomed to seeing women as aesthetically appealing/decorative -> people believe women's bodies are more attractive. Combine that with, over the last few centuries in Western culture, a society where women were not encouraged to express sexuality or sexual desire, and many male relationships, even platonic ones, became suspect. The imprisonment of people like Oscar Wilde and Alan Turing for 'sodomy'/homosexuality, the phenomenon of adding 'no (pejorative word for homosexual here)' after expressing an opinion about another man, the use of 'gay' and other words as pejoratives, used especially towards boys when I was growing up, the disdain that accompanies anything perceived to be feminine as weak, vapid, brainless and lesser - it all adds up to a situation where any kind of positive expression by a man about male bodies is strongly discouraged.
The same wasn't true for me as a girl; I did get asked if I was a lesbian when I'd say I didn't care if I got married, and didn't want children, but it was never the same kind of stigma and bullying as the 'effeminate' boys at school got. I can't ever recall meeting a woman who was uncomfortable expressing an opinion on another woman being pretty or beautiful, because there's no automatic assumption that the attraction is sexual (which probably makes life more difficult for lesbians and bi women since it's like they don't exist, but as I have only ever felt attracted to men I can't confirm that). I have met multiple men who refuse to acknowledge other men as handsome, even as a thought exercise. I think this is changing, again, but it hasn't totally gone away.
Edit: removing a filtered phrase and trying to explain it some other way!