For IPFS vs CDN, I'm guessing relevant copyright laws give a service provider an out when it's a well-defined user/customer doing the copyright-related redistribution; no such agreement exists for content on IPFS.
EDIT: Trying to read the relevant DMCA sections and precedent makes me happy I'm not a lawyer. Cloudflare was previously sued for copyright infringement (Mon Cheri Bridals, LLC v. Cloudflare, Inc.) and found not guilty. In Cloudflare's own blog about the decision, they said the suit was meritless for several reasons including "our services are not even necessary for the content’s availability online." My guess is there is sufficient ambiguity over whether operating a inter-protocol gateway puts them at increased legal liability.