SF is a favorite because of faulty public perception. That's how Vegas makes it's money. ESPN, NFLN, and Peter King, et.al. slobber over the 49ers from the final whistle of the packers game until kickoff the following Sunday at 1 pm. That influences public view of SF. "They must be the better team because Peter King and Trent Dilfer said so!"
Joe Public hears this shyt all week and goes out and drops $100 on the 49ers as a "lock."
Then the game gets started and the panthers win. Vegas cleans up and the square bettor loses because they drank the media kool aid.
Point spreads don't often have anything to do with who is the better team; they are adjusted up or down based on human psychology and perception of a team. The sheep blindly follow the cocksucking talking heads and lose. It happens every week.
That's why SF is favored - an angle for Vegas to win.