So I'm assuming we are looking 6 years later from when a 10 year old had Ms. Marvel posters all over her bedroom walls. If Carol was still using the name presently, would this noob have adopted it? There are two Hawkeyes, and what's with that kid running around calling himself Powerman right in front of Luke Cage after Luke had to beat the shit out of Goliath to earn it... it's funny how Hank Pym never bothers to stop supervillains from taking his costumed identities. What the hells up with that?
It's a question of necessity.
Being a child with no money (Spider-Man's costume still makes no sense.) Kamala goes through her wardrobe only to find an old halloween costume to use as her super hero costume after the shit hits the fan in the second act.