I think part of the reason is this. Many traders who have profited hugely from the bear market aren't bitcoin proponents, they're traders. they're excited by a new, inexperienced and unregulated market. They want dollars and, percentage wise, they profit more on the way down than on the way up. I'm not real sure about the miners continually dumping argument; sure many would do so to recoup costs but others would be looking to hold in hope of future gains.