As long as Bitmain sells every one of the miners they make they can charge as much as they want. Free market capitalism at it's best. Think about how fast each batch of the S9 miners has "sold out." Would you lower your prices if you were selling everything you made? Probably not, and you might even raise your prices to see how much more you could make. Oh, sure, some of the people buying the miners will complain about the price, but at the end of the day they still sent the BTC or used a credit card to buy them.

If/when another company selling equivalently powerful miners arrives on the scene is likely when you will see prices moderate.

Cheers,

- zed