redhawk23, I think from a storytelling perspective, audiences who haven't read these comics for years like we have need a valid reason for these characters to dress up in tights and masks. Because the prevailing belief is that like tights and spandex in live action look like some cheesy comic book character.
So the reason is that if a vigilante is on the streets, he needs to be wearing a costume for a reason. If Matt Murdock is facing thugs who have knives and guns and weapons, what happens when he gets hurt? Now realistically a monthly comic book doesn't have to deal with that a lot. Or if the character does get hurt or injured he pretty much usually miraculously heals up.
In a TV show, well the format is different. The style is sometimes a bit more visceral. So when you see these characters in flesh and blood, how do you deal with OK this character has been messed up and is hurt badly. He doesn't want to wear armor because it would slow down his fighting moves. But now he has a protective lightweight armor costume that provides him more full body protection in his war against crime.
I assume with things like Captain America, they tried to give him a suit that keeps the stars and stripes but looks more functional and utilitarian. It's more like something a soldier would wear but still has some of the iconic elements. But if he's a soldier shouldn't he wear a helmet with some armor instead of a cowl/mask?
That's my long-winded answer.