It does seem arbitrary but I think the answer might be far more mundane than conspiratorial; There is simply no legal authority to hoover up the data of and trace back to american citizens for 8chan type websites.

I don't know man, even if the NSA, FBI etc couldn't give a shit about the legal implications, Cloudflare as a public company and it's officers would have legal liability if they violated the law.

Wild conjecture I know :)