They say the best coaches shine the brightest when given extra amounts of time to prepare for an opponent, and Rick Pitino is perhaps the best college basketball coach ever in the Sweet 16.
The best sleepers are those that come out of nowhere. If everyone is taking the same upset pick, then the overall benefit of picking it—either in your bracket or at the sportsbook—immediately diminishes.
Furthermore, it sort of defeats the purpose to pick against a better team that comes into a game with a mental edge it otherwise would’ve lacked had everyone not doubted them.