Because.. it's battle shonen lol
Let's be honest, japanese shonen thingy (anime, manga, video game) is still trapped by the idea of 'oh let's make the main protagonist relatable with the audiences' and let's be real majority of shonen thingy is kids, teens, and young adults. So.. yea it was to be expected the main proragonist would be kids or teenager, MEANWHILE.. they develop a story that supposed to be applied to an adults, and what happened next is.. they just didnt care, just put the kids or teenager main protagonist into a plot that supposed to be for adults, no one would care anyway
This is where japanese anime/manga lost to western comic. Western comic have characters like Batman, Wolverine, Iron Man, Hulk.. they are not kids or teenagers but kids and teenagers still love them, they didnt have to relatable by age with their audiences and it works perfectly. I think japanese author should learn about this and not repeating the same formula for decades