Well I don't know much detail but Bieber was basically the male Taylor Swift. I think they came to prominence around the same time. Taylor Swift is still a huge star, Bieber not so much.
I know he was throwing tantrums on stage, photographed in bed with a hooker, some silliness about egging people's houses (lol), some other hijinks.
I don't know it just seemed like he was right on the cusp of transitioning from teeny-bopper act to major pop figure, much like Justin Timberlake did. Imagine if Timberlake was receding and diffusing circa 2001? People would have laughed and thrown tomatoes if he tried to put out a song claiming to bring "sexy back." I'm literally lol-ing at the thought of it. It would be like an Ali G skit. People would laugh their heads off. So yeah, that's what Bieber is up against. He isn't perceived as having the musical chops to survive male pattern baldness and still be taken seriously. He's not Brian Wison.
Tl dr
Bieber balding = David Cassisy and Leif Garret career
Bieber fullhead = Justin Timberlake career