With Satellite 6.3, installation media are no longer created when syncing a kickstart repository. This is working as intended and was introduced with bug 1382775.
I'm turning this into docs BZ, as provisioning guide still works with the fact that the installation media is creates on repository sync https://access.redhat.com/documentation/en-us/red_hat_satellite/6.3/html/provisioning_guide/configuring_provisioning_resources#Configuring_Provisioning_Resources-Creating_Installation_Media
*** This bug has been marked as a duplicate of bug 1566135 ***