They usually aren't. Both Balthazar and Castiel know that. It's part of their game, part of their scene. Giving Castiel the ability to be cold, empty perfection for Balthazar to ruin and reassemble.

"You don't know bliss unless you're all the way down his throat and have him hold eye contact, truth be told."

It's not a lie. Balthazar has rarely experienced anything that hot, and he's had plenty of orgies in the past.