Potentially someone could actually prefer Hyper-V on Windows 10 over VirtualBox. On my Windows 10 laptop I use Hyper-V to run Docker, stand alone Ubuntu 16.04 and Gentoo VMs, as well as Windows VMs provided by whatever the Modern.IE project is now known as.
I'm sure that if I needed to run something much less currently maintained, like OS/2, that VirtualBox on Windows would be better.
Also, I think it would have been a good idea for the Docker for Windows package to allow choosing between common Windows VM system instead of being tied to only one.