Many more people are betting, so that there are not enough bets to balance out the reslult. Bookmakers have suffered severe wins and losses on such big tournaments, some have gone bust. Traditionally in a state of enthusiasm many people bet on their own team. Not so much professional betters, but those who only bet for big events and want to express their enthusiasm in some way. Then it is the outsiders.
Many people like to bet on outsiders they believe are good enough to surprise.
One has seen Japan in a good match, another believes strongly in Norway to advance to the finals. So if one of those cases comes true, bookmakers will lose. This is why they adjust the odds of those teams a little although they cannot adjust them much. Otherwise they will suffer a drop in turnover. We take the example of Intertops.