Package manager

Hi don't know if i put in the correct product name. I have REHL(developer subscription) on an external HD and Fedora on my main Hard Drive. This question is related to booth because they are the same family. The disros i have used before are Opensuse, Arch, Manjaro,CentOS and Kubuntu. They had only one package manager Opensuse uses ZYpp(Think SLES uses another not sure) Manjaro and Arch uses Pacman and Kubuntu uses APT like all Debian based distros but REHL, CentOS and Fedora uses two Yum and DNF why? I can booth type for example sudo yum install gparted or sudo dnf install gparted which one to use YUM or DNF. Sorry mabye stupid question but i am quite new to linux in general yes i used Linux in the early 2000s but i was young than and than you had like mostly 3 distros Red Hat, Suse and Mandrake before Ubuntu. Red Hat was my very first disro than Suse.