Why was Dokou a "count" and not "Darth" or something

Count Dooku is only called a Count by most people because gained the title from his family. He is also called Darth Tyranus by his master (Palpatine)

My guess ( Im a moderate-smart) as far as knowing the Star Wars facts of life. But my guess is because he was involved with the Sepratists. He was Darth Tyranus. But when he joined the Sepratists movement, my guess is he wasnt fully for the Sith or the Jedi. Cause thats what the Sepratists are. In our world they would be Independents. IDK, best guess.

yea as a normal person he is a COUNT but he does have a sith name that isnt said very much although palpatine makes up a story about darth tyranus in episode three

Actually dokou has a darth name its mentioned in the atack of the clone. I think palpitine say it before the seen of anikan and padmes wedding.