Because kids are stupid.
Kids will all jump on the bandwagon. Never been any different there. That's why the best soldiers are 19 and 20. They don't think critically and they jump on the bandwagon. Example, WW1, blow the whistle and run over the top right into machine gun fire. If you told me to do that at my age, I'd tell you, "you do it". But kids will do it because it's like being on the football team and their buddies all do it.
I'm well past my teen years. I would never have done something so disgusting as this article. But I did do dumb things. I recall VERY WELL in High School in Hamilton where there was a guy who was gay. He wasn't rumored to be gay. He was definitely gay. Word got round instantly. He left the highschool because of the heat. But a few years he came back to finish High School. That's when I was there. He was probably 2 years older than me, but I remember he was in my French class. This was the 1980's in Hamilton. That kid was TERRORIZED by hoards of bullies. Some really tough tough hoods just ripped into him at every chance. I remember this one kid who was a real mean nasty piece of work, very big, very strong and we were in gym class and he kicked a soccer ball at the gay kid so hard it would have broken concrete. Not once, but repeatedly. Some joined in, some (like me) just watched and snickered and did nothing. It was the law of the jungle. You didn't rat because next time, it would be you. I regret that incident and the terror that that gay kid faced. Though I never hurt him, didn't bully him, I never helped him and I didn't try to make friends with him either. (He could have used a friend I'm sure.) I regret my behaviour from back then. But I'm older now and I'd like to think wiser. But my point is that the teenage brain is more childlike than adult like. They say the brain does not full mature until about age 25 and I believe it. (Not that that justifies this sort of abhorrent behaviour.)