It's less overhead and better integrated into the system as a whole. After all a VM is still a separate entity in its own environment. WSL is jumping over the fence and runs Linux stuff in a Windows environment.

Think of it the other way. Why would you use wine if you could just run Windows in a VM? :)

I don't know if I would call it better or worse, it's more about preferred workflow. I'm typing this on a MBP and I have a fleet of VMs specifically because I'm tired of playing the platform game. I can configure a VM specific to an app's needs faster than hosing my host OS with a very specific configuration that may not match production environments. Even with version managers like rvm or nvm/n there is just a lot to get wrong. It may be faster or less resource intensive to not have to spin up a VM but I've been in .NET land with desktop apps and now various web platforms enough to prefer this workflow. For someone like me, this would be for personal usage versus job related activities but I do see the benefit of having the choice. I just hope I'm strong enough to resist the temptation because my personal win10 laptop is a graveyard of rails installer and a few other various barely-supported toys.

you don't pay for RAM that the VM doesn't use and don't have to deal with madness that is sharing files over sftp/smb/nfs/shared folders/etc.

Because it's a fraction of the resource cost, and shares resources better with the host system as well?