So what's your explanation?
Who knows? But outside of rare exceptions (like the Ramirezes Hanley and Manny) no major league player is ever 'dogging' it, especially one in a slump, doubly especially one who just signed a massive contract with a lot of concomitant pressue, and trebly especially one like Werth with a well-documented history of hustling and busting his ass.
Werth is doing poorly, that is beyond dispute. But the reasons for it have nothing to do with a lack of desire or complacency on his part.