* Multiple machines are a larger attack surface and a larger surface area to get things wrong.
* Overhead. It might be getting smaller but it's certainly still there. Not just the application but all the OS services that are duplicated are extremely wasteful when you're billed for your resources directly.
* Your vendor distributes applications as docker containers.
* Your developers are building and testing in docker.
* Clustered resources are dead simple with swarm. It can obviously be done with VMs but it's work.
* Devs and sysadmins alike enjoy using off-the-shelf services that are maintained by someone else.
There are enterprise use cases where docker makes sense if the app support people are less impossible to deal with than the SAs. But you don’t have that issue in cloud.
