Wonder if this is because Bitmain holds so much BTC and is hard to cash out this much... so can sell in large numbers but 1000BTC min trade WOW.
Bitmain is best opening there own exchange or a new kind of service to help cash out.
Thats basically less than 30 units/day. It makes sense to set a high minimum to see who steps forwards. Trying to offload that on an exchange would require many small transactions and likely drag the price down if done in a short timeframe. From an accounting POV, having a signed contract of BTC->FIAT between two parties is the legitimate way to do things and will benefit both parties.