Yeah... For dudes. They're like that to look cool for other dudes because that's what dudes think is cool and movie makers want their superheroes and leadmen to look cool to their target demo, which is usually also dudes and little boys.
They're not doing it to market to women, which you can tell if you look at how these actors are shown on magasine covers targeted to men vs women. On the men's covers these guys are ripped to the gods, muscles out, shirts off, on women's covers, they're usually wearing a shirt, or even a t-shirt, something that looks nice on them, covering up a bunch of those muscles, and look either friendly or generic model pose.
Some straight women love muscle men, but even then it's quite rare for "muscle men" to mean the 1-10% body fat ripped guys, usually it means "he goes to the gym 3 times a week" people. It's so, so far from being a universal rule and the superhuman extremes pushed as the norm aren't even attractive to most women. Gymbros are getting most of their attention from other straight men.
