Is there any reason why there isn’t a separate downvote button next to the upvote button?

I know that there’s a flag button, but I’d use the flag button only for abusive content. I’d use the downvote button with the posts that I don’t agree with or that don’t provide much value, so that they get hidden, which would remove the clutter quickly.

Steemit can get copy features from StackOverflow. They have some good features to moderate the community with a functional rewards system.