As an operator is a cluster-wide API, and a ClusterImageCatalog is also a cluster-wide API, it makes sense that a user interested in a ClusterImageCatalog would prefer to install it alongside the cnpg operator in a single helm install.
This way the user can install the cnpg operator, and then immediately reference any needed ClusterImageCatalog without having to install it standalone in a separate helm install, or even worse as part of a helm install for a namespaced cluster.