Preface: I am not attracted to kids!!!
I'm gonna get roasted alive for this but here we go.
I honestly think that, like a lot of other issues with humanity as a whole, this boils down to the fact that a lot more people are attracted to kids than they'll ever admit.
I see it the same way with rapists and abusers. No one's gonna openly talk about being like that so they don't get caught but the fact that it's so common tells me it's not out of character to be done. Especially looking at history and how commonplace it was for grown adults to marry underage kids or sell them into sexual slavery.