I don't know the specifics when it comes to the physics of it, but analog NV amplification simply has more sensitivity than digital image sensors. Of course, you can still analog-amplify an image onto a camera sensor for further digital processing, but I don't think that's common.

The particular case that you describe - automatically adjusting to ambient light - is handled adequately by analog circuits; this is called "auto-gating", and is pretty much standard nowadays.