Because several cops did what they were trained to do individually. When you are rapid firing you are not counting your shots. Most of the time trained to double tap (2 shots) because criminals who have been shot once have been documented to return fire many times and take out the officer. It’s not tv where the first bullet kills you.
To make sure, you, the officer, walk away without Joe violent blow returning fire, you make sure he’s down and stays down.
Now you have more than one officer doing that same thing. Making sure the threat is ended.
MAKING SURE the threat is ended. They didn’t say ‘ok you shoot twice and I’ll shiit twice’ each of them shot individually, as many times as they knew would make sure the threat was ended.
This is often why, if you have more than one officer there in the threat situation, that someone can get shot 19 times or so. The Leo are trained to individually respond and take care of the threat. So they all respond to it, and each one who responds to the imminent threat, makes sure the threat is ended.