It sticks in the memory of the listener much better than complicated policy issues.
For example if Christy had gained traction, Trump would have said something like "I know and like Chris, but I do worry about this health...you know, carrying around all that extra weight.
Trump can say why does Hillary not wear skirts on the campaign trail? Is she trying to tell women no one would take a woman seriously in a skirt? Of course we would all know he was referring to her giant clankles.