The total hashrate for BTC has dropped 50%. Mining BCH has become more profitable. I see that major miners like BTC.TOP have stopped completely mining BTC. As a result the average time between blocks has gone up to almost 20 minutes. It will take time for the difficulty to adjust for this and than it will be profitable for miners to start mining BTC again. Miners will switch back to BTC because it is in their interest to do so. Bitmain is still mining BTC because they don't want to see the value of BTC to drop.