There are lots of reasons.
When I was a child, kids would be teased for being too fat, too skinny, wearing glasses, you name the reason. But the teasing was limited to just a few schoolmates. Now with technology the whole world knows, or at least that could be a perception.
That doesn't or shouldn't have any thing to do with it. I was the "fat kid that wore glasses" and had what was called a "girls" name. Picked on all the time by the kids. And had an abusive father. I'm 65 and never killed anyone. And own, what some would say, too many guns.
Around the time time Dr. Spock's book stated to be followed as the way kids should be raised is when things started to change. And generations since then things have got worse. Kids are taught that they are not responsible for treating others good, and they should do what makes themselves feel good. When was the last time you heard some one tell a young person to obey the "golden rule"?