I think it is just a dearth of younger actors that can portray the way we see Hokan. It's funny, I was watching The Avengers with my son yesterday and thought of Samuel L Jackson to play Hokan. Of course he is also somewhat long in the tooth, though not as much as some other nominees. Plus casting him would cause a rip a hole in the time space continuum because he already played Mace Windu. Again, even though Hokan is able to take on clone troopers he seems to be written as someone older I think, and I am not sure that was KT's intention.