The difficulty has soared since they were launched, so much so that the latest batch will probably never make a profit (even with the modded firmware you're still only looking at $4-5 a day after power and that will only get worse with time) and so people are selling them when they arrive to try and cut their losses.

That and the fact you can sell it on eBay when it arrives and use the money to do stuff like buy x3 Vega 56 cards which combined will make double the BTC/USD per day of a D3.