Speculating, but Apple wanted to make sure that the only people photographed using the headset were models and actors who are very attractive. That way whenever a news outlet runs a story about it, they have to use the picture of the attractive/cool people using it, and people make an association that the headset makes people attractive/cool.

Why is that significant?

This seems like exactly what Apple would do.

The passthrough face requires a face scan thing that wasn't ready yet. For controlling avatars viewed in a virtual mirror I think I read they gave you an avatar of someone else to control.

If the passthrough eyes were available, clickbait journalism would also probably do things like intentionally cross their eyes and get a goofy look on it, then write and article about how the headset will make you look extra goofy.