Why doesn't Bitmain put 100% of the D3's they produce to work mining as soon as they come off the line vs. selling them to the public?

Is it because all their mining warehouses are at capacity and they simply can't find/build additional locations to mine with them to keep up with the rate at which they produce them?

I have read the stories about Bitmain "testing" them for weeks/month before selling to the public.  But if they are still producing $100/day at that point, why not just keep mining with them?  Perhaps the Chinese government has some sort of export mandate forcing to sell at least a certain percentage of them?