Now, it's my contention that Bargnani's trade value peaked in the summer of 2010. Back then, you could have argued that he simply hadn't been given a chance to shine (although I would have argued against that) or some of the other many arguments his defenders used that summer. It wasn't a rare opinion that he might finally be able to measure up to the potential he apparently had. And then he was given the chance and, while he certainly was able to score at a good rate, his season was considered by most to be a disappointment, mostly due to his lack of development on defense and on the boards.
Now we've got one more excuse. That Bargnani simply needs a good defensive coach to kick his butt. Not nearly as many people are drinking the Kool-Aid on this one, but there are enough to show that people still believe he has the potential to be a better player. Maybe not great, but better. Even you.
The problem with that is, what happens if he DOESN'T improve? What happens to his trade value, then? You are right that GMs tend to gamble, but the more excuses you cross of the list for Bargnani, the less likely a GM is going to want to gamble on a guy who arguably doesn't even have a positive effect when he's on the floor. If you've got an asset that probably won't go up in value much, if at all, but has a better chance of going down, then the smart thing to do is trade that asset for something else.