This extra steem is largely being stolen away from the mega whales. Many of them wouldn't upvote always, but these rewards are still capped at 9.5% steem produced annually. Also notice that your voting drops faster.. this means you have less full powered votes per day. So for the super powered vote, you are robbing your total votes. 9.5% annually, is like 40 million in STEEM paid annually. This is where it is coming from. The mega whales were holding back their votes, and it was a practical thing... hard for a whale to vote on every post.