Witnesses are already doing things for voters / users but it's not obvious from the typical user's point of view, especially if he doesn't understand blockchain and DPOS. The majority don't even know what witnesses are, like @sebbbl said.

The goal of the program is, by upvoting directly voters / users (providing an actual, visible, immediate reward for their implication), to encourage them to broaden their vision fo Steem and get interested in the participatory democracy it proposes.