Why are teenagers so selfish and only care about themselves?

I watched a tv show and two teen girls yelling at some little kid to go away. Then they find out that the kid ran away so many times and his mother passed away. One of the girls said, “Yeah but guys he EMBARRASSED us!”
The other said,” I’m sorry. But still he embarrassed is in front of our friends.”
Wow I couldn’t believe them. They only cared about their own feelings instead of that poor little kid. The mom said, “Oh so a little boy being lost doesn’t matter to you girls? The only think you care about is looking good for you your friends.” Something like that.
I’m glad I wasn’t like that as a teen.