Because HPV isn’t airborne and highly contagious like all the other vaccines.
It is not airborne, but it is contagious, and once you get it, you can pass it on to others for the rest of your life. So even if you don't get cancer, you can infect others and give them the risk of getting cancer.
Look, I admit that Perry takes a hit for the Guardasil issue, but he has clearly and publicly said he made a mistake - I think the damage will be minimal. It's not like tonight is the first time people have heard about it, and he still has a major lead in the polls.