Over a 31-game schedule, a college basketball team is bound to have some letdowns. Not every player is going to bring the same energy level all the time. Not when you're not getting paid to do this, when you have to deal with academics and other distractions off the court. It's simply unrealistic to expect the team to deliver the same effort every night. Some nights, guys are just going through the motions. That isn't to say that they don't care about winning -- just that, well, some games are more important than others. Everybody knows that.
A classic time for a low-energy game is when the team's just had a very high-energy one, or a series of them.