neo9436 is dead on, too much supply.
Which can also be phrased: No incentive for consumers to buy and use Bitcoin.
The real problem is this. The 'real problem' isn't the 3600 coins dumped by miners.
We are 6 years into this, and consumers still don't give a flying f** about Bitcoin, and have no incentive to buy it.
That is the real problem. Lets focus on solutions for that instead of whining about the miners selling coins.
-B-