YUM v3 is no longer developed, having been superseded by DNF for
several years. With DNF now available as a usable package manager
in Red Hat Enterprise Linux 7 through the Extras channel and
SUSE Linux Enterprise 15 through PackageHub, there is no reason for
keeping support for YUM v3 around.
We are keeping support for requesting YUM because in Red Hat Enterprise
Linux 7, DNF is referred to as "YUM v4", and it is simply referred to
as "YUM" in Red Hat Enterprise Linux 8. To avoid confusion from people,
we're just going to leave it in place as an alias to the DNF package
manager.
As for why this is happening now, Fedora is retiring YUM v3 in
Fedora 31, so we might as well get it over with and cut over now.
Reference: https://fedoraproject.org/wiki/Changes/Retire_YUM_3
