The point is people who buy votes get there money back. Even in the extreme example of someone promoting post 200$ every day, they still don't lose ROI and will eventually hit a point of being able to recycle without needing to buy more Steem. So yea, it may be a short term price increase but that is it, and when the person is done promoting steem, they can dump all the funds they used to buy votes back on the market. Free advertising dosent work well in the end.