They made their own choice. They chose family.

Castiel is good at research. More importantly, perhaps, he likes research. So when Sam pitches the suggestion, he sits up a little, as if tentatively accepting something that feels like a reward. But he knows he needs to be careful. It's a task, a purpose, not a gesture of good will. He'll do well, and then maybe he will be praised.

"I can do that. I would like to do that."