I'm not qualified to say that one was more culturally divided than the other, but if I were to say it I think a geographic argument might be made. Italy is thin and stratified N-S, with seas to either side and to the south. Germany is rounder, and historically has had aggressive neighbors to the E and W. Not to be a German apologist, but if you had France on one side, and Poland and Russia on the other, you'd probably do well by working together to defend yourselves. That's not to say Italy hasn't ever been invaded, but an area with coasts is easier to defend than a relatively landlocked area smack in the middle of competing empires, with little to no real geographic barriers. The more precarious German situation probably made them less able to admit cultural divisions.