Why? I suppose one possibility is that any PR is good PR, so why not do what you can to get some press during the dog days? More likely, though, is that this is as good a sign as you're ever going to get of just how little difference there really is between the two. They desperately want to differentiate themselves, but they simply can't find something of any real substance to disagree about. So rhetorical trivia gets the place of honor instead.
It's better than nothing, I suppose. But it would still be nice to know if there's anything serious on the foreign policy front that they disagree about. So far, I don't think I can point to anything.