Because it’s accessable, and is also the extent of my knowledge in running a VM. I won’t speak about KVM because I am not intimately familiar with KVM, nor will I ever be. I’m certain it’s a better solution than VirtualBox, just as running games in Linux with Wine/Proton is a better solution than setting up a VM to game in.
I’d be happy to hear about the details of why KVM is so superior, if you’d care to enlighten me! I’m always looking to learn new things.
The real question is why we’re down voting people who are adding to the discussion just because we disagree with them, instead of just having a conversation?