How can I uninstall Oracle Virtual Box for good? Virtual machine images still present after uninstall

I uninstalled Oracle Virtual Box with 5 VMs on it but when I reinstall it back, I still see the 5 VMs?

That's because uninstalling Virtual Box does not delete the virtual machine images you created while using it.

By default, VirtualBox stores its VM files in the folder VirtualBox VMs in the user's home directory (so, typically under C:\Users\<username>\VirtualBox VMs on MS Windows). To get rid of the VMs you created, you can delete these files (if you are certain you no longer need them).

Note that you can store your VM files in other locations, too, if you select a different location when creating the VM, or in the VirtualBox configuration. Then you'll have to look there.

See the documentation for details: 3.1. Where Oracle VM VirtualBox Stores its Files