I can tell you.
all it takes is a few people w/ big bankrolls to get the ball rolling by placing some bet bets. then it all trickles down the pike and gathers steam along the way, and near the end it gets to NFL forum idiots who think they can handicap sports, who in turn convince themselves that is is very important and must join along, who then proceed tell people to play the side where the "perceived" sharp $$$ is coming from