All varsity sports in the ACC have to crown their conference champ via a conference tournament. It's as simple as that. It makes the ACC money and is great for the fans. It is difficult for the players and coaches because it means another game (and probable loss) against a top tier opponent who you have already faced once that year. For the bubble teams, it takes away an opportunity to play a "weaker" non-conference opponent to improve a team's chances of making the big dance.