You somehow have some disabled repositories.
Execute this command: yum repolist, and you should have an ouput like this:
…
base/7/x86_64 CentOS-7 - Base 9,363
centos-sclo-rh/x86_64 CentOS-7 - SCLo rh 6,002
centos-sclo-sclo/x86_64 CentOS-7 - SCLo sclo 467
epel/x86_64 Extra Packages for Enterprise Linux 7 - x86_64 11,882
extras/7/x86_64 CentOS-7 - Extras 451
nethforge/7/x86_64 NethForge 7 109
nethserver-base/7/x86_64 NethServer-7 - Base 146
nethserver-updates/7/x86_64 NethServer-7 - Updates 379
updates/7/x86_64
…
You need to enable centos-sclo-rh and centos-sclo-sclo repositories:
yum install yum-utils -y
yum-config-manager --enable centos-sclo-rh centos-sclo-sclo
Then, reinstall nextcloud.