I think the difference is that men are more physically violent. Boys fight and throw punches. This doesn't translate well to Instagram. If teenage boys spend more time online and not in person, then they have less opportunities for physical violence and abuse towards each other. However, it's different with teenage girls. There's more emotional abuse and pressure to look a certain way. Instagram and social media are a very efficient way for this type of abuse to take place, so it prospers there with young girls.