They are trolls or idiots downvoting.
Thanks ~

Downvoters are free to do as they wish, but since there is no obvious or stated reason they are just losers.

Personally I think free downvoting should cost a lot more RC than normal voting. Also Steemit should remove their 20sp delegation from these dumb accounts that don't engage by posting or commentig and just give out meaningless 10% votes or whatever up or down.