Cancer? No by all accounts he a is a good human being.
Bad fit? I'd say yes. CV is was he always has been. A face finess scorer who avoids contact like the plauge. A dcent rebounder with the length to block shots on occasion but with no instinct for or inclination to play defense. He's simply a bad defender IMO. While he's a good person his motivation and work ethic have always been under question.
The issue with the Bucks is that while a good player Bogut is more of a high post finess center. Paiering him with a guy like CV simply makes them too soft both on O and D. CV would be much more effective with a physical good defending Big man so he could spread the floor, grab a few leftover boards, feed the post (which he does well he's a good passer). He's kind of a glorified Donyell Marshall or a more skilled much worse defending Horry really. Put him with Yao, or Howard and watch him florish. Or you can stick him on a bad team and watch him put up some numbers. He's basically giot to play PF becuase he's too waek for centers and he's so bad on D he can't check SFs. I think thwe Bucks have seen enough to realize he's not going to change.