It used to be. They moved to a VM.

Turns out that it's easier to emulate a CPU than syscalls. The CPU churns a lot less, too, which means that once things start working things tend to keep working.

> Turns out that it's easier to emulate a CPU than syscalls

I don't think WSL2 supports CPU emulation. It might not even support (or at least rely on) driver emulation, though Hyper-V itself does.