That market cap is illusionary because there's no way to deposit BCH into exchanges right now. ViaBTC apparently requires 20 confirmations which would take about a week at the current hash rate, the other exchanges like Kraken and Bittrex aren't accepting deposits at all and don't plan to for a few days yet. So essentially all of the BCH making up that market cap cannot in fact be sold at all right now; the only BCH can be is from Bitcoins that was in exchanges that support BCH at the time of the split.