I see it more as a title - I mean, in the beginning they always said "The" Makuta. It worked at the time, but once the Species and other members were introduced, he needed to get his own name. It's similar to saying the king or the lord. If there is only one person to talk about, you don't need a specific name, but once you introduce several people with the same title, e.g. "King John" and "King Richard", you need to make a distinction