Because any gear that isn't running at 0.25W/ghash or less is no longer producing and profit and after the next diff change in the next 24 hours it will certainly be at a loss. There was an estimated 400 petahash of gear that should be shutting down over the next couple months. Looks like about half of it has just turned off. That or network variance. However considering that build out of new gear is still happening and hash rate is going down perhaps variance can't account for a decrease. Either way .. mining with anything but the S7, the latest Avalon and BW.com's 14nm miner thing will effectively cost more than it will mine even with fairly cheap power.
Depends on your electric cost. My remaining S5s are still profitable - though not by a LOT - at 7cents/KWH.
I'd suspect it's more about Bitmain shipping their next batch of S7s (there's always been a noticeable drop at that point as THEY stop mining with them but it takes a week or two to get them packed up, shipped, and the recievers to get them back in service) with possibly some addition from other folks selling and shipping miners like Avalon.
Might also be that one or more Chinese ISPs are having some sort of connection issues the past week?
One thing people should keep in mind is when they are profitable but not by a lot... it's normally a good time to sale. Price of sales will continue to go down and will do a big drop once next gen hit's market.
I was barley profitable on last gen (avalon 4.1's, sp20's, S5's, S5+). I sold them all and bought coins with them for the temporary future. Eventually they will go back into mining gear but I made a heck of a lot more by selling then I would have by minin on tiny profit.
