So, you have the top 2 teams in those 4 conferences playing what is essentially a play-in game to the playoffs.

You could easily have a team that has clearly "won their conference" in terms of having the best conf record, and even have previously defeated the #2 team.

Now, it's not actually about who really is the best team in the conference, it's about who wins that particular game. The #2 team can win in an upset, thereby effectively advancing themselves to the quarters.