Because Sam is a douchebag full of himself and his own stupid needs - and let me tell you Lucy couldn't have chosen anyone better to fill in as he was already half way there.Dean's pleasures are mostly venial (xcept gluttony, but again, he said he had really suffered from hunger...)
Sam's are all capital sins (a.k.a deadly sins).
I'm sorry I don't want to antagonize anybody (and of course I have nothing against the delectable Jared) but Sam's behaving like ... *self censored*