Probably because they didn't read it in People Magazine or watch it on Bravo. Run an ad showing what has happened to Christian bakeries. Just because Santorum believes those things doesn't mean it's all he's about.
I remember in 2012, Santorum gave a speech on the economy. He was then asked about a social issue and he answered. Then he was asked why he talks so much about social issues. I don't see it in his speeches. He takes positions I like on these issues, but they are not the entire premise of his campaign.