I think a lot of people don't understand well the witness system. Steem is complicated. Everyone don't know what is a witness, how it works and that votes can be casted.
Some never vote. Some vote progressively a few witnesses during their journey on Steem. Some want to support the community voting the top witnesses and are voting by mistake Justin's witnesses. There are also a lot of dead fishes that have already voted and won't change their votes.