Workflow for openstack deployment using kolla and kubernetes

I was going through :

https://github.com/openstack/kolla-kubernetes/blob/master/specs/ansible-deployment.rst

I am wondering why ansible has been choosen for workflow automation instead of openshift as for most of containerized applications we can define a workflow through openshift and from there kuberenetes handles the lifecycle of pods. While I am excited about the project , I am having this doubt in my mind. For example, we can define a workflow in openshift to install all the kolla controller specific containers and then once they are successful, we can deploy the compute specific containers. This may actually show-case the power of openshift(kubernetes) and kolla. Just wanted to know your opinions on the selection criteria.