Its because our wide receivers suck...and our online can't protect long enough to give Cam time.
O-line isn't good, but it isn't as atrocious as people on here make it seem. At least two of those sacks against the Saints were due to Cam holding on to the ball for too long. He needs to start running or throw it away earlier. That said, the right side of the o-line needs to be addressed this offseason.
EDIT: There was also at least one sack where Cam didn't step up in the pocket and the tackle did his job. Like I said, o-line isn't good but there are times when Cam isn't helping them.