At cloudflare's scale I can imagine that for many websites, compressed data falls out of cache frequently and then the file has to get compressed again on next

At cloudflare's scale I can imagine that for many websites, compressed data falls out of cache frequently and then the file has to get compressed again on next request. For example if you're hosting a website that contains a ton of different news articles or user-submitted stories that's probably tens of thousands of separate blobs of text, and each one might only get read a few dozen times a day. The odds are much lower that the individual content is going to be in cache on the particular edge node that handles the request. The CDN is still useful in this case of course, both for ddos mitigation and because it can cache the common stuff like your website's stylesheets.