Earlier quoted context omitted.
Real talk though. Why does it matter? No skin off my back.
Are you looking for an explanation for existence of insider trading laws?
> Illegal insider trading refers generally to buying or selling a security, in breach of a fiduciary duty or other relationship of trust and confidence, while in possession of material, nonpublic information about the security
Bitcoin Cash is not a stock or a security, so it's questionable whether this concept even applies. But even if you considered it to be a security, then how is Coinbase's decision to list Bitcoin Cash on their exchange somehow in breach of "a fiduciary duty or other reltionship of trust and confidence"?
Perhaps there is some other SEC regulation they might be violating about how the operators of exchanges can trade on their own exchange, such as front running, but it doesn't seem like that would have anything to do with insider trading.
I agree that it's possible that Coinbase's decision to begin trading this asset could influence its value, but that doesn't make the action insider trading. It's fine to take actions while expecting to influence the value of an asset - see for example the massive short position that Ackman took against Herbalife. His public media campaign to discredit the company was expected (calculated) to drive down the value of their stock, but is the fact that he took out short sales in advance of that action "insider trading"? No.