What's easier - managing cloud costs or managing a datacenter or co-located physical hardware and setting up and maintaining all the functionality you need to do proper CI / deployments / monitor uptime / data analytics?
So you run your own services on their hardware (as opposed to using cloud SaaS, where you rent both the hardware AND the service).
We're comparing an ideal version of cloud to practical versions of on-prem. When the ideal version becomes practical, it might be a no-brainer. But for now, companies are going to have to do what's best for them today.