The answer is simple : They know a lot of people are going to dump BCH now and the price is being pumped by the BCH supporters in the beginning. When all the hype has passed and everything has been dumped, BCH will trade at much lower prices and they would not have to take such an huge knock.
I predict that BCH will be trading at between $20 to $80 per coin soon and that would be manageable for most exchanges.
They took the safest option to protect their business and to see how successful BCH will be, before they step in to reap the trading fees.
I agree that the price of BCH will drop to double digits by the end of the year. However, they will continue to survive as their hashrate is 25% of what BTC has - even tought that % diminishing a lot through time and it also depends on the total reward the miners can receive. In the longer term, the price might go back to low triple digit from general acceptancy by the exchanges and investors. Roger Ver may start to promote BCH to become a broadly accepted currency like BTC.
By the way, everyone were thinking that Coinbase will start to support BCH
at the end of the year, but it may be or may not be true. Coinbase said "by" the end of the year and not "at" the end of the year - which means that it may happen any time before the end of the year. They said that to allow themselves more time to test their platform with the new coin. This experience will be very benefiticial to them as they can anticipate the next coin split better in the future.