Reason #3: They don't have a song together that warrants a Grammy performance.
If Chris Brown and Rihanna do a duet at the Grammys, what song are they going to do? "Cake"? Ugh. "Nobody's Business"? UGH. Sorry, guys. But, you don't really have a collaboration that deserves to be performed on the Grammys stage this year. So, how about saving the shared performance for next year? That'll give you plenty of time to come up with something epic to perform. And, it'll give all of us the chance to come to terms with the fact that Chrianna is back together again. Assuming, of course, Chrianna really is back together again.