The simple answer.
State vs Cong. Dist.
Not only state v congressional district, but a state where a lot of the citizens do not pay attention, versus a congressional district where everyone is consumed by politics and government. Big big big diff. When Cantor strayed, everyone knew it because everyone follows that stuff, without Brat having to buy ads to tell people.
Graham strayed and strayed and strayed, and a lot of good ole boys in SC never realize it.