Explaining what's going on would require communication, and Dean definitely does not have a degree in that. Plus that seems to take away from the whole vibe. Chuck's supposed to figure it out on his own, with Dean gently nudging him, locking him in traps, etc. along the way. Then he'll give him a pop quiz on comprehension at the end. Totally makes sense.

"Not yet, but you'll figure it out." He gestures at him. "Or, you know, you won't. You'll thank me later."

He grins and then turns to leave.