jsDelivr pulls from Github/NPM - I am unsure if they then permanently, locally store the file or if they still have some reliance on GitHub/NPM being up.
With cdnjs, we store all versions ourselves and have no reliance on GitHub/NPM for fetching resources from the CDN - GitHub is only used by us to publish new versions/libraries which are then cloned to the Cloudflare origin servers.
This is currently how our infrastructure is set up, we publish resources to the central GitHub repository and then Cloudflare clones that to the origin servers. We try to ensure all the popular packages are available whilst filtering out packages that aren’t popular and would only waste disk space.
We have plans in the works to make the process of requesting new libraries to be added far easier than it is currently.
Let me know if you have any more specific questions