In a bracket pool, the goal is to finish with more points than everyone else. That is not the same as picking the most correct teams. When you pick a popular favorite and they win, most of your pool scores those points too. A pick can be correct and still do very little for your standing.
The Optimal Bracket measures the gap between what the analytics models say a team will do and how often people are actually picking them. The bigger that gap, the more you stand to gain when that team wins.