A good analogy for the reason why glass is not bulletproof are crumple zones in cars. When a car is being driven at high speeds the car is travelling with a lot of momentum and will carry to do so if no opposing force is applied (Newton’s first law of motion). Deceleration is calculated by change in velocity over time taken, if the car comes to a sudden stop the deceleration will be great because of the short time taken thus increasing the overall force. We know this because Force = mass X deceleration/acceleration. Crumple zones absorb the energy so it is not transmitted to the occupants of the car.
This is the basis for bullet-resistant glass. Non-reinforced glass can't extend the time taken for the acting force by elastically deforming
This is the basis for bullet-resistant glass. Non-reinforced glass can't extend the time taken for the acting force by elastically deforming