Keeping with the times would have meant more multi-cultural casting. You mean in keeping with the old times? Way I see it is, the novels left the make up of the good races themselves open ended, but Hollywood/Jackson decided to go through stead fast with the White people play the good, Dark people play the bad thing.
Even fictionally speaking, it seems stupid that over thousands of years not a single one of the darker people of the other races (Easterlings lol) have migrated or mixed with the White folk of the West, Rohans, Elves, Drawrfs, Hobbits, Gondorians etc.