Being a proxy and cache is their business. All it takes to set things up that way is then a little bit of configuration that points to the actual origin.

I think if they would be an official mirror there would be a fair amount of more work being involved. Eg you can’t just randomly wipe the cache anymore and need to have higher persistence guarantees, since you are not supposed to refetch from other mirrors all the time.

They have Cloudflare Workers (with limited disk space), but act as a caching proxy is still the main business of Cloudflare. So i think acting as a proxy make sense for Cloudflare.