So, the role ended up in the hands of Sam Worthington. Matt Damon went about his normal regularly scheduled tasks, and then suddenly Avatar became the highest-grossing movie of all time in one summer. Unfortunately for Damon, he used that time to finish the Bourne Ultimatum, which flopped HARD.
Charlie Hunnam, Fifty Shades of Grey
Hunnam would have been in Fifty Shades of Grey if it weren't for his insane schedule. Between shooting Sons of Anarchy, and Crimson Peak, Hunnam got overwhelmed by his workload and decided to pull out of one of his projects. That project ended up being Fifty Shades of Grey.