Master Didge hit the nail on the head, it is helpful when we consider a sneeze has long been associated with the onset of some fearful illness. Wishing "good health" or extending a blessing seems the humane thing to do. There are countries like China and Korea where the custom is to say nothing. Barbarians.
In Italian, it comes out as the rousing response of "Salute! " -meaning "Health". Easier to say than Gesundheit