Why do you suppose it is that kids who are into anime tend to have an almost exclusive interest in dark, violent, and morbid types of anime and manga?
Growing up (6th grade to senior year) I liked comedy in my anime and drama in my manga (mainly because drama meant beautiful art).
Teen angst ain't it? I think we all used to be like that at one point - I know I did but I grew out of that eventually!
It's hard to say and I don't think I'll ever understand it all. Similar reasons girls (both genders these days I forgot how old I am) cut themselves when having no real issues, pretend to be bisexual when they are more interested in one gender over the other, act like their interest or thoughts are unique to the world and misunderstood. Just kids being kids I guess, look at attack on Titan for example, it has one MAJOR FLAW that one piece had back before its release and despite never fixing it, STILL LOVED BY ALL. The story even did a huge fucking 180 after the obvious plot was moved on and well......kids will be kids.
Don't question it just enjoy the silly moments
They're impressionable. They're young so chances are that they haven't seen anything with actual plot or detail that speaks to them (or they don't have the life experience to enjoy/appreciate more emotional stories than action stories). So they see a character gain abilities out of nowhere and kill a dozen people, then they go "Wow!! Cool!! He did all that!"
Lol, I remember loving things like Ninja Scroll, Berserk, Samurai X, ect when I was young / in my early teens. I don't know, I guess it just seemed really cool watching violent things, the same reason I loved violent video games. Like, it was so cool to own and play the GTA games maaan, "Cause my mom let me get it I'm so cool!". I mean I liked good stories and diversified my genres even then, but nowadays I seem to definitely appreciate a good story more than I used to. I think it's just pretty normal for kids to be curious about things that are like, taboo and stuff.
I didn't like Beserk when I was younger cause I didn't wanna watch poor shota guts get his cave explored, but now that I'm a man of refined taste I love it