Also probably because taking a role in an action based drama as the main character/lead is insanely exhausting and a lot of hard work that most don't want to do. Take JCW on The Worst of Evil for an example, he mentioned in an interview that he once promised to not do action ever again after The K2 but only did The Worst of Evil because he loved it so much and said that it was really tiring and exhausting afterwards, he said it was a lot of hard work because of the choreography and training the body in an action packed drama. So you can apply the same to Vagabond if one of the actors/main lead wanted to forget about Vagabond.
