I had girl friends who did it to get attention from their parents/boyfriends/classmates. They acknowledged it back then. It wasn't some secret. It was essentially for attention, aesthetics and the light headed feeling. I still have an A4 page somewhere with a big ass heart drawn on it by an ex with her own blood. Kids are just weird when the hormones hit. The cute/creepy ratio of that painting has definitely gotten worse with time.
TBH kids tend to be edgy for a bit when puberty hits. The emo generation had a ton of girls cutting themselves for attention for example.