How is 70% of the mining power directed at Bitch Coin? Did Bitmain hijack every Antminer on the planet? No miner in their right mind would voluntarily mine that crap. How did they get that much of the hash rate?
Why would do you assume they will not voluntarily mine BCH? They see this as an opportunity to get much more money for electricity spent. It will be over in a few hours anyway:
Coin Date (UTC 24h) Remaining Change
BCH Nov 12th, 21:09 3 hours, 2 minutes (131 blk) +400.00%