Bynum? Larry Sanders?
Bynum - Injuries
Sanders - He had a fat contract when he decided to retire. That was all him. And teams would probably still pay money for him if he came back.
As for the questions about how Rondo's tenure ended in Boston ... were you watching the same team? For one thing, even before his injury he was turning into a more and more numbers-oriented player who didn't actually seem to make his team better and who didn't get along very well with his coach or teammates.
Then, when he came back from injury, he gave what appeared to be maybe a 40-50% effort. Less than that on defense. Rather than embracing the opportunity to be the leader of a rebuilding squad, he set a bad example and loafed his way out of town. With, of course, the lovely parting shot about actually needing to play defense now that he had joined a decent team.