[int_19h]

You can, but in a VM, you still have two different and separate filesystems, and then some mechanism to provide a window into one from another (custom FS driver mounted in a directory, SMB share etc). In WSL, there is only one filesystem.

And it's not just filesystems. We're also talking about potentially shared file descriptors/handles (where appropriate), access to processes in both directions etc.

So from user's perspective, I would argue that it's actually more similar to Wine. Even if the implementation is more low-level (syscall emulation vs userspace API emulation).