Yes, as I noted you can have swap, but it is not typically done because a VM that is swapping will take away resources from other VMs in a way that's harder to contain. VM services I have bought have disabled swap for this reason.

There are many reasons for virtual machines. And if you could get it to work properly, swapping would actually help the resource allocation. However, there is no virtue in any event of having every VM use of the ram for its own copy of every running binary. Sharing this ram would benefit all VMs and the system as a whole.