I would be wary of exchanges. If you look at Stamp, for over a month, you see huge sell walls placed at intervals. And to withdraw that much of fiat, the exchange would require your identity and bank account. So, the key person to know why the huge btc quantity of sell limit order is the exchange owner.

Many people are speculating why the market has been so bearish. If the bitcoin news websites are smart, they would bug the exchange owners for answers. Think about it, all we can see are just the orders and transactions. The exchange owners are able to see who are placing these orders and making these huge transactions.