It really is, and Sam would love to. But he's very mindful of the fact that Castiel is more than a little turned around at the moment.

Sam drops the towel around Castiel's shoulders, reaching up with one hand to cup the other man's cheek. "I know that you can," he says softly. "But you don't owe me anything, Castiel. There's no need to repay what I give to you freely. Nor do I expect payment. That's not what I'm about."