That tendency goes way back. Elvis was a rare exception. In general, tween girls are not ready for a "bad boy" or a manly man. They want to chase a boy, but they want the boy to be "safe". Leif Garrett, David Cassidy, Andy Gibb, Michael Jackson, Justin Bieber -- girls were not afraid that these fellows would take unfair advantage of them.
And, yeah, as someone already pointed out, the queers REALLY like these teen idols just the way they are.
...and don’t forget Bobby Sherman!
True, but Bieber makes Leif Garrett, Bobby Sherman, David Cassidy, even Donny Osmond look like the Marlboro Men in comparison.