I guess what that tells us is that people who place their money where their mouth is think that the Rams are a whole lot better than the Niners and ought to win rather handily.
The betting line doesn't consider "any given Sunday" because there's no way you can predetermine if a team is going to come out flat, or have serious injuries to key players in the game or as in GB, come out with guns blazing only to fade in the 4th quarter.
Add to that, the Rams have proven to be about the best road team in the NFL.
So other than for emotion, there's little reason to see the Rams losing this game.
If any team is open for a let down it's the Niners having given it their best shot on MNF, having everything go their way, moving up and down the field almost without resistance and STILL losing.