The problem is here every person have own definition of quality post that's why they are downvoting you even you written very good post which can help steemit to gain more visitors. one of my friend also get downvotes even she written seo friendly + quality post with low competition and high traffic keywords. And it was about technology. and she get downvotes by some so called spam cleaners (whales). they prove your mistake even you don't does any mistake. They just want to downvote anyway. They are feeling jealous to seeing your reward.