The whole idea that the home team gets an automatic 3 point is nothing but false.
The whole idea behind Vegas created lines is it's just an attempt for them to get even money bet on both sides of the bet. Typical lines are -110, meaning to win $100, you have to risk $110. This is called the "vig" or the "juice". If you consider a bookie's viewpoint, let's say he gets $550 on the Cowboys +2.5 and $550 on the Commanders -2.5--and let's say that the Cowboys win. Those bettors that took the Cowboys, in total, risked $550 and profited $500--but the Commanders bettors risked $550 and didn't win anything. The bookie pays out $500 to the Cowboys backers and then pockets that extra $50 he makes.
So yeah, the whole "home team gets 3 points" is nothing but a myth. Vegas wants even money on both sides to guarantee profit on their part, so lines are dictated by public perception and nothing else. If money is getting one-sided, the line will often move in order to tempt more bettors to venture to the other side. Has nothing to do with what "vegas thinks" or "vegas' prediction", it's ALL about public perception.