I agree that Trez is really making an effort. Against Sampdoria, after missing 2 good chances, he even drifted back in our defensive 3rd and tried to press/harry. A rarity, no? His bashers would only be too keen to point that out as another reason to trash/get rid of him but I'd like to take that as a positive sign that he wants to do better in a Juve shirt. The self-consciousness, followed by sheer frustration triggered a positive reaction. That's good, isn't it?
Why is Trez doing so badly? A few possibilities, IMO ...
The team changed its tactical approach and I don't see ANY evidence that we're better off so far. Trez is a direct consequence of this. As the lone striker in our current set-up, he absolutely has to be there and about for any possibilities. Strictly speaking, he has NO business doing anything else considering that the opportunity cost could well be a goal. Again, its all too easy to pour scorn on how many he's scored this season but in all honesty, the service/support he has been receiving has been quite pathetic. Which of our strikers have actually done as well as we expected them to? Doesn't that then point to something deeper than an individual problem? Like those before him (Vieri, Henry et al), lose him at the club's own peril ...
Stagnation. We saw it with Zambrotta, who was mediocre for years before finally exploding into the player we know today. I don't think its far-fetched to say that some of us have been spoiled by the fantastic record of Trez in his 1st 2 seasons. If anything, it makes his current slump look worse than it actually is. I think he'll be back better than before. I think it'll be pretty soon if Juve ever decides to fix her various other problems. I can only hope he'll still be in a Juve shirt when that happens.
Contracts, money, frustration etc as some have already covered so well.