Both underdogs covered again , when the Chiefs were up big I knew it's not over as their defense tends to loosen up in the second half.
To cut down on injuries, teams apply the bare minimum needed to win. Then coast to preserve their player's health.
Kansas City has such a powerful and overwhelming offense. Their defensive line is prone towards falling asleep thinking its ok if they lose focus, their offense will bail them out.
Chiefs might have peaked in their game with the buffalo bills and began celebrating too early. They didn't prepare for the bengals the way they would if they were facing a bigger name team. They probably thought they would defeat the bengals easily and be in superbowl 2022 guaranteed.
All of these failings combined can converge to form the perfect storm necessary for underdogs to overcome the odds.
That said, this has been a strange season for the NFL and for the NBA as well. The normal skill gap which normally separates players and teams, appears to have narrowed considerably.