Obviously, you do not understand "the room" which is how and why the sports books in Las Vegas operate at a profit. So, let somebody who lives in Las Vegas (and who also is close to people who have made a nice living in the industry) try helping you to understand what goes into oddsmakers setting the betting line. I'll try to keep it so simple that even you may be able to understand it.
Sports books exist to make money. As such, they try to attract bets that are split 50/50 dollar-wise between the two teams. Why? Because the their "vig" is usually 10% of the total dollar amount being bet. In other words, they get to keep 10% of the money for themselves regardless of which team wins. Call it their commission. They establish the spreads to get as much money as possible being bet as evenly as possible on both participants. Sports books could win or lose big if they deliberately tried to get bettors to bet in a lopsided manner. Instead, they adjust the spread leading up to the game to influence where the books want the betting money to be placed. They don't "like" teams the way you like teams. But they do like your money. They want you to like your team enough to bet on them.
Let's look at some betting factors that involve both the Cowboys and the Packers. Both teams have many die-hard fans who will bet on their teams purely out of sentiment. It's akin to voting (with money) for their favorite team. The sports books love this because of the vig. But other bettors bet to win and have little sentiment other than love of cash. The more bettors the better. Keeping it split 50/50 is the trick.
The spread can both encourage that more money will be bet in total and also that more money will be bet on one team or the other. Remember the vig. So, when the books increase the spread it may be to get more money bet on the other team. For example, the home team being favored by three points is a given. When the spread is adjusted up or down it is meant to influence the betting. If the bets are balanced the spread may be adjusted to help maintain that balance. If you see the spread shift before Sunday keep that in mind. The spread is influenced by the power rating and also by how the bets are being placed. Betting dollars may outweigh the power ratings.
Ever wonder why the spread sometimes includes a half point when no games ever end up being won or lost by such a margin? If you haven't figured that out yet then you may need to remove the Stetson because it could be restricting the flow of blood to your brain. But in case you have no idea here's one important reason why: Should the scoring differential set by the books and the final score of the game be exactly the same, 3 points for instance, it results in a "push." It's a tie of sorts. That means nobody wins (that placed a bet under that spread). There goes the vig on those bets. The money goes back to the bettors. All of it. That displeases the books. And here's something else that you may not know: You can buy points either way in the spread. I'll leave it to you to figure that one out. Hint: Think vig.
Las Vegas books love no team. It"s strictly business. But please continue clinging to that misconception. By all means visit us and place bets with your heart. Besides building billion dollar+ casinos with your losses it helps to lower my taxes.
Hope to see you out here real soon.