the simple answer.... because they can. The market will bare it.
At this point there are really only 2 options for home miners... Bitmain and SP and Bitmain is less than SP.
But you cant even buy antminers now...
Can buy C1 and S5. Just no more S3.
S5 is sold out.
Its just for the holidays, everything proper shuts down at this time.
Bitmain shows C1 available to purchase but won't ship until after the holidays. The S5 is in a sold out status. I see their top offering is hosted S5's on Hashfast.net but those are sold out as well.
I wonder what the Bitmain supported S5 farm means as far as quality of any S5's offered to the public in the future.