To an unemotional NFL bettor the Cardinals are the better team. Look at the trend of the last 25 or 30 games for both teams and determine which is the better team? Cardinals are much more likely to win this game than the Rams, hence the money moving to the Cardinals, and the spread moving to encourage money on the Rams.
Too much emotion ruins making money betting on NFL games, the trend is your friend. You will miss on a game here and there but overall you could prevail (or maybe not lose your a**) following what a team has shown that they are.