Is it radio airplay? Yes
Is it label support? Yes. Leppard has far less label support. Which of course translates to radio airplay.
Is it that the women adore Jon Bon Jovi? Yes. This can only help. People are delusional if they think that BJ's success can be attributed solely to the strength of the music.
Is it the strength of the material? Not really, after 1992, both bands have produced some great material and some really crappy material. It's a tossup.
Is it that Bon Jovi is American and Def Leppard is British? Yes.

So the answer is the combination of all those.