Because they felt it was unfair for their owners/slave masters and other white people to vote and not them since they were treated as slaves, worthless and trash, so they fought for the right to vote so they can be treated equally like others so no one can be higher than another, or own someone in a matter to speak.
Well, the vote was always biased. Since they couldn't vote, they wouldn't be able to choose the best one for them. Even when the got to vote it was biased, because the KKK would bully them into voting for who they wanted them to vote for.
