I think that by adding more and more and more shots, earlier and earlier, and all at the same time ... they have reached a tipping point because people are questioning why their children need so many shots when they did not need that many as a child themselves.
One friend of mine, a mother of 8 children who range from adult to 5-yrs-old, said that the reason she started skipping many of the vaccines is because she could see how from one child to the next they kept adding more. She was stumped at why each successive child would be in "peril" without more vaccines than their older sibling had had. She jut didn't want to jab them so much so often.