1. Because it.s not a real thing that was recorded, there are no sounds.

2. It would be dangerous to break real glass.

3. It could hurt the actors and it would be hard to do retakes.

4. A real phone wouldn't sound as clear.

5. The sound wouldn't record well and there would be background noise.

6. The hit's wouldn't make as loud of a noise and the actor would get hurt.

7. It's up to how they interperet how a fictional thing should sound.

8. The microphone would get damaged or it would land on whatevers protecting the microphone.