All additional concerns and requirements that you need money, time, and people for. I'm not claiming a server-as-a-service / cloud has zero skill requirements, but it's a lot less than managing your own hardware.
I can't comment on total costs / costs over time though.
I do devops work for people, and clients using cloud services consistently have more devops issues than those on dedicated hardware.
In my experience cloud deployments also need documentation and processes. It is of course a different set of documentation and processes, but cloud's not magically free of these requirements.