Years ago, when Docker and Docker Hub was starting out, I didn't really understand why is the thing not built to allow super easy self-hosting/proxying. It seemed crazy to me that one company is hosting full OS images that needed to be downloaded over and over again, especially for CI environments. Linux distro ISO images always had mirrors, even torrent distribution. Whenever I tried looking at caching Docker Hub images, I gave up and just accepted the wasted bandwidth.