Don't shoot the messenger, I can't verify this, but apparently CBS gets two doubleheaders a year, one Noon-3:30 and one 3:30-8.
They are using their 3:30-8 doubleheader this weekend, meaning for the first time since 2010 (except in 2011, they had both be 3:30-8, and Alabama-LSU was one of the two), Alabama-LSU won't be the CBS prime time game. Last time was for Alabama-Florida in 2010.