That's where the cartilage was. You can find that hole in your own skull easily enough. There should be a small bump midway up your nasal ridge. That point is called the rhinion. Everything above it is laying on your skull. The parts of the nose below it cover your nasal cavity.

Because the bottom half isn't bone and the whole thing is hollow.

Anatomically correct skulls have an hole where the bottom of your nose is and the eyes are both smaller and higher up than you probably think.

https://en.wikipedia.org/wiki/Orbit_(anatomy)#/media/File:Ey...

Looking at yourself in a mirror, if you hold your finger over the top of your nose your eyes will see under your finger. Move your finger just low enough so you’re seeing over it and you should be touching the bottom of your nasal bone. At that point your nose should be more than a finger width froward from the bottom of your orbital socket which is where the hole in skulls starts in those skulls.

Look at a picture of a skull in profile. You'll see that there is half a nose, not no nose. That half of the nose that you can see is the bony part. The missing half is the cartilaginous part.

Why is there a hole? Because your nasal canal extends inside your skull to connect with the back of your throat. I guess I don't fully understand the question there.