@kornboi
I meant, that in Marvel comics/movies often plain and sometimes not that good looking people get super powers and pretty sexy over night. And in my opinion this is basically the same thing.
I don't think that the mangaka had some bad intentions by doing it this way, it's just more appealing for a wider range of possible readers when a plain guy/girl gets some cool powers, saves people and turns into a hottie.
And like
@hyoretsu said, the actors have to get to a lot of dieting and training too to fit their roles. They're more appealing too, when they're fit and good looking.
And it's not like looks is everything, when someone has a shitty personality they can be as good looking as they want, you wouldn't think of them as attractive or appealing.
You get my point right?

It's like with Cap, the heart counts.
But dude, I'm so jealous of his skills. That communication skill and the Item Box, so useful! And the other stuff too
