Even if they could make transactions, the exchanges aren't accepting deposits of BCH. The only exception I'm aware of is ViaBTC and apparently they want 20 confirmations (about a week at current hashrate, I think). The BCH market cap that's quoted in this article is rather misleading because nearly all of those coins simply cannot be sold on exchanges currently.

Regarding the question in the replies: when the fork happened, all the BTC in the exchanges at the time split off into an equal amount of BCH. The various BCH/BTC markets are effectively trading people's claims to portions of those much smaller pools of BCH that were already on the exchange when it forked. (Those claims can't necessarily be converted into actual BCH yet either; for example, Kraken isn't currently allowing BCH withdrawals.)