The eternal battle of Law and Chaos, the movements of the planets in the void of space, they're all just steps in a cosmic ballet. You are the only person aware of the music of the spheres that this cosmic ballet is set to, and you are entrusted with making sure that good experiences tragedy before triumphing over evil, pleasing the ballet's empyrean patrons (A.K.A. the players). If they knew about the music, they may loose their way and step out of line, so you must do anything to prevent that from happening.
In this take on bards, they are attempting to make sure that the players accomplish their mission while never finding out about the massive play (of sorts) that they are taking part in. Their magical powers come from having their actions harmonize with the celestial music that drives everyone else's actions. From this, they can vastly increase their natural abilities, and sometimes even perform wholly supernatural acts. If ever a PC finds out too much about what's driving their actions, than it is the bard's job to make sure that the PC doesn't think too hard about the implications, or to stop that particular line of thought in its tracks.
TL;DR: Bards know about the 4th wall and want everyone to put on a good show for the players.