Why would a robber completely empty out a broken window?

Long story short I found out my car got broken into this morning. My rear driver's side window was completely shattered, all the glass either on the ground or in the car. I'm fine and nothing was stolen which almost annoys me more.

My question is why would whoever broke the window completely empty it out? It almost looked like the window was rolled all the way down with how there was no glass in it. Most of the glass was outside the car. Is there a reason that they would completely empty it out?