Because they realized they can make more flipping them than mining with them... 
Its a new device... that makes no sense...
1st batch is $1000 with PSU... so, flipping it for $1500 is better than mining?
It was $1999
https://shop.bitmain.com/product/detail?pid=00020180503154806494uGcSyiu806FD
Mother fucking flipper are putting pre order for august batch with their margin. They are middle men for idiots who don't know they can buy directly from bitmain at a lower cost
Example :
http://vi.raptor.ebaydesc.com/ws/eBayISAPI.dll?ViewItemDescV4&item=332680682812&category=179171&pm=1&ds=0&t=1528988900675
But if people are stupid enough to purchase a used product with almost no guarantee that will have a ROI even longer than a GPU and that will kill the network, why not profit of their stupidity ? Right ?