Superhero costumes aren't exactly the most flattering: their material tends to be light-weight and flexible for combat and impact, and an impressive physique is pretty much the easiest mark of heroism to identify. You'll never see a portly Superman, or a "plus-size" Captain Marvel: that's just how audience's minds work.
So it's no surprise that some superhero movie actors have been through some serious transformations to fit aesthetic expectations. They've put their pay-cheques and bodies on the line in the short-term - avoiding treats like carbs and laziness - to look like the demi-Gods and villains on the page.
Yes, they might have the best nutritionists and personal trainers and the kind of spare time that makes transformations an awful lot easier, but the dedication to changing for what amounts to a game of make believe is no less astonishing.
And it's no wonder they're then more happy to show their physiques off in normally unforgiving spandex (or less).
Other actors have gone through different changes: making physical sacrifices to fit into the role no matter how they might look in the short-term. That deserves as much praise.