I assume that some people run RHEL but don't want to pay Red Hat. Red Hat don't provide
binaries to such people, but nothing stops you (a Red Hat subscriber) from taking most RHEL
packages and uploading them to a public FTP server, this isn't even illegal, at least for the
vast majority of packages. People who download those packages have only the RPM signature to
rely on to prove that they're authentic rather than being trojan code you uploaded to exploit
them. Whereas you, as a subscriber have the additional protection of Red Hat's site security.
There's no good reason to do this sort of thing when CentOS exists (and when RHEL
subscriptions are comparatively cheap), but then there's no good reason to climb Everest and
plenty of people do that too.