From a "decentralized internet" point of view, I wouldn't like to have a mirror going through a "big" CDN like Cloudflare. Morever, actual mirror are plenty enough and fast enough.
On top of that, Cloudflare's HTTP firewall may block some apt-get/curl/wget users which is not wanted for software repositories.
Also, Cloudflare's Terms of Service state they're explicitly meant to be used with HTML content.
2.8 Limitation on Serving Non-HTML Content
The Service is offered primarily as a platform to cache and serve web pages and websites. Unless explicitly included as a part of a Paid Service purchased by you, you agree to use the Service solely for the purpose of serving web pages as viewed through a web browser or other application and the Hypertext Markup Language (HTML) protocol or other equivalent technology. Use of the Service for serving video (unless purchased separately as a Paid Service) or a disproportionate percentage of pictures, audio files, or other non-HTML content, is prohibited.
Even "cheap" CDN providers are more expensive for high-volume traffic when comparing to dedicated servers with unmetered bandwidth, and many servers are hosted by universities with large amounts of bandwidth.