There are also more BTC exchanges to manipulate than Bitcoin Cash or Alt coin exchanges, so these Alt coin whales can concentrate their efforts for better results on only 1 or 2 exchanges where these coins are traded.
This is going to happen a lot more now, since this was such a huge success for these Pumpers, so be wary.
But one need to understand the core of this manipulation. It isn't Roger and team alone who contributed in manipulation but the big BTC community who started selling their BTC and buying BCH. I ain't able to understand how can someone invest in Bitcoin if he doesn't even has patience to hold it for single loose day!
Bitcoin community on whole is too weak because of huge influx of amateur traders. That is the main reason why we see easy manipulation and high volatility everyday.