Using a FQDN is less likely to be unknowingly hijacked when it's a domain they control and use daily. URL references also contain the version number, typically

Using a FQDN is less likely to be unknowingly hijacked when it's a domain they control and use daily. URL references also contain the version number, typically an immutable Git tag reference. They also benefit from just needing to download the source code that's referenced and not the entire package. With Deno you can also optionally host versioned 3rd Party packages on their deno.land/x CDN. URL references are also cached locally on first use and can be used offline thereafter.