That's not the best example really.
Swift wasn't 'down on confidence', he didn't want to be there. And he made a pretty ballsy decision to quit, and good on him.
You could make the argument that a lack of support from the fans or whoever made his decision easier but that misses the point - once a player has convinced themselves they want out, I think it can just be better for everyone to move on.
I see your pov but I don't think that not wanting to be there and being down on confidence are necessarily mutually exclusive. I think that being being down on confidence tends to lead to not enjoying the situation which in turn can lead to wanting to leave.
I don't think Selwood is playing bad because he wants to go to Geelong. I think it's more he's not feeling great about the way he is playing and is now thinking if he'd be happier elsewhere. I think the latter situation can be turned around pretty fast, unlike the former.