Just look at Cryptocompare trading volumes for Bcash. On Bitfinex only BCH volume 24H is more than $18 million. It's roughly thousands dollar trading fees per hour. I don't think it's a revenue that exchange business would shrug off as negligible.
It might not be negligible value that can be generated, but you have to remind yourself that a lot of exchanges are not as big as Bitfinex and thus their expected revenue from BCC fees would be relatively lower than a few thousand per hour. But at the same time exchanges, when they take fees for both buying and selling, need to be sure they will actually make money off of selling their BCC and they won't lose the money they were gleaning on fees.It makes sense really, no point throwing what might end up a shitcoin onto an otherwise reputable exchange. There might not be a long enough life for BCC to justify adding it to most exchanges.
traders are picking up the coins that are being dumped and the exchange is earning a good amount of money as commission and so it is a win situation for the exchanges and not the other way around. 
Why would they want to miss out on those?
