I suspect that the real problem isn't the type of content but the fact that it is being requested by robots at a high rate. If you had a text file that humans were actually browsing and reading I doubt Cloudflare would care, but humans read files at a much lower rate than is occurring for this text file.

Say you do that and I DDoS the easylist.html. Cloudflare will start applying their DDoS mitigation. Now everyone's app receives the Browser Integrity Check instead of the list.