VM based backup application as well as OVF exports use the latest state (snapshot) of the VM. The backup/OVF basically consolidates the snapshots.
If you want to preserve the snapshots you'll need to manually download the files from the datastore using e.g. WinSCP/FastSCP. VMware Workstation supports the ESXi hosts's virtual disk format and you may just need to make minor changes (e.g. network configuration) in the VM's settings.
André