The obvious has been discussed and argued over: the comics fanboys like cheesecake, and the (male) artists like drawing it. They don't care as much for looking at guys. Screw practicality: titties sell!
There's a hell of a lot of truth to this. Still, I don't think it explains everything. There's not just an abundance of scantily-clad women; there's a corresponding dearth of scantily-clad men. And I don't think that dearth is explained just by the fact that artists and fanboys don't like scantily-clad guys.
Here's something I belatedly realized while strolling around and observing scantily-clad people of both sexes in public: in one of the odder aspects of our culture, women have more socially-acceptable options for scanty clothing than men do. By which I mean: women can show some excess skin in public and look appealing or glamorous, but men who show excess skin in public look... how to put this? ...like dorks.
Here's an experiment. If you're wearing a button-down shirt, undo the top couple of buttons and go look at yourself in the mirror.
If you're a woman, you're dressed daringly, which will get you some (possibly unwanted) interest.
If you're a man, congratulations. It's not everyone who's brave enough to hearken back to the days of disco.
What do you think of when you think of barely-dressed male comics characters? Ones who show a lot of skin? Yeah. That's right. You know who I'm talking about. Hawkman. Aquaman. Friggin' *Namor.*
These characters do not look strong, virile, or (what's really important to the straight male reader) cool. They look *silly.* Hawkman carries the shirtless look off best, but that's because he's got a huge, beaked mask to distract you from the fact that his leather Playtex bra lifts and separates. The only male characters I can think of who have regularly gone into action shirtless or nearly so and looked really cool doing it are a) Colossus and b) the Hulk, and neither of them look especially human at the time.
Well, okay, you ask, but what about strategically-revealing clothes? I mean, a lot of female heroes currently bare their midriff. Couldn't you have a male hero wearing a costume that bares, say, a selective amount of skin?
Yeah. You sure can. It's called *Nightwing's first costume.*
(Heck, go watch Rocky III's beach training sequence for a non-comics example. Sylvester Stallone and Carl Weathers are out running in the surf. It's the 80s, they're both action stars in terrific shape, and they've got the montage thing going -- they should look cool, right? Wrong. Because (especially in the early, out-of-shape Rocky sequence) they're wearing cut-down midriff-baring tops.
Um, yeah. "Less than manly.")
In fact -- and I admit this seems increasingly weird to me -- the more I think about it, the more it seems that the scantily-clad male characters in comics have some kind of inhuman appearance or an alien cultural background. The Thing is a rocky monster; the Hulk is a green one; both are beyond worrying about their fashion sense. Hawkman has been reincarnated from a variety of cultures, and he's occasionally alien, plus he has the friggin' wings. Thor, who wears a dinky vest and bare arms, is an ancient Norse god. Kraven the Hunter, Ka-Zar, and Sheena, like their loin-clothed progenitor Tarzan, are rooted in the jungle (while the Black Panther, by contrast, goes clothed head to toe -- perhaps because he's a modern Black hero, as much as an African one, and the thought of him running around barely clad was a little too much for editors' liberal sensitivities). Namor and Aquaman are Atlantean heroes. Lobo, who wears a vest but no shirt, is the last Czarnian.
Maybe they just don't realize they look like dorks?