"They have been unable to effect the same thing with Sam. I don't know if it's because the writers are themselves at sea about Sam and Dean's relationship, or because Jared can't convey subtle emotions the way Misha can, and so they wind up writing lines for Sam that never feel genuine or heartfelt."

It doesn't help that JP is quite possibly bored of playing the Sam that most of the audience wants to see, he just wants to play Bad!Sam or some other F*'dUp!Sam and when he doesn't get what he wants he's incredibly half hearted in his performance. In certain episodes he actually looks bored, with his hands in his pocket and this nonchalant couldn't give a crap demeanor. Then when he wakes up and decides to put in a little effort he seems to overcompensate and plays it hammy.