I don't know if this applies to Dareus, but I don't know how many people here are aware that many NFL players don't actually like playing football. It hurts - a lot. I'll never forget hearing an interview with Chargers D-lineman Burt Grossman on the Jim Rome show over two decades ago. In response to the question of how much he still loved the game (he was nearing the end of his very solid 6 year career, in which he had 43.5 sacks), he essentially said that he never liked playing in the NFL and only did it for the money. Rome then asked him if college was the last time he liked playing. He said he hated playing in college too (he went to Pitt and was drafted 8th overall in the first round). He closed by saying that the last time he liked playing football was in high school. He had stuck with it because of the money.
Kris Jenkins' NYT piece from a few years back is quite revealing about the punishment DTs take: http://www.nytimes.com/2011/11/20/sports/football/kris-jenkinss-view-of-life-in-the-nfl-trenches.html .
Consider all of this when thinking about Dareus, who is effectively set for life. The only financially stupid thing Dareus could do at this point is retire, because he'd forfeit millions of dollars. Even if he's unmotivated, he needs to stick it out to collect that cash. Again, I don't know if he hates playing football, but he might. We as fans are justified in not liking this, but this sort of situation is more common than you might think. It's why teams are terrified of guaranteed contracts. This ain't MLB w/regard to "love of the game."