Let's say you break out of a web app on a VM, then as the local user you exploit the kernel. It's the VM host kernel. You have root on the VM. The VM is running on a full virtualization platform, though, so you'd need to break out of the VM to hit other guests or the hypervisor.

Linux containers run a new environment on top of the host's kernel. It's the same kernel in one container as another and the same as in the host. If you manage to break out of the namespace or otherwise exploit the kernel, you're already in some other container's business. Worse, there's a good chance you've exploited the kernel in a way that you can get all the other containers and the host all at once with one exploit.

Assuming the attacker already knew the IP of every VM, and they were all running the same kernel with the same exploit, and they were all exposed to the internet, it would be similar...although you would have to repeat the steps 'N' times. Or, assuming you could somehow escalate your VM kernel exploit to a higher level hypervisor exploit and get to the top.

That's not usually the case, though.

With containers, you get the kernel exploit, and you're in, for the most part.