When I was 16, I used an unloaded gun to scare a younger boy (age 14) into taking off his clothes and letting me put my penis in his mouth. I was consequently charged with rape, assault, kidnapping, and numerous other crimes. I plead guilty to one count of first degree rape and spent the next twenty years as a ward of the state, over 17 of those years in prison, where I myself was violently raped and repeatedly assaulted. So when you ask me what drove me to sexually assault younger kids as a teenager, I just want to laugh. Your question (and accompanying comment) is biased and ignorant. I can't even begin to tell you all the reasons why it is impossible for me or anyone else to answer, not to mention the fact that even if it could be answered, it wouldn't help anyone stop it from happening again. The only thing an answer to a question like this ever could accomplish --- which is what I think you are no doubt attempting to accomplish by even asking --- is finding something or someone to blame for what happened so that you don't have to face the ugly truth that you yourself are no different than me insofar as we are both, presumably, human, and equally at fault (though neither of us, or anyone else, should be blamed).
Yet, I don't blame you for asking either, because I understand why you would, just as I would, if I were in your shoes, so to speak. Just as you would have done the same as I did when I was a teen if you were in my shoes. Realizing this truth, instead of evading it the way your question does, is the only way we will ever come to understand such behavior together. We must understand it together, because it is something we did --- and continue doing --- together.
So, if you are really seeking to understand, as you claim, then as yourself what exactly would drive you to "rape" (or "murder", for that matter). At least then you'd be looking in the right direction for answers, inside yourself, instead of outside yourself for something or someone to blame.
[J.D. August 31, 2018]