They use a form of plastic inside the glass for the windscreens which makes the glass shatter proof. They don't use plastic solely because plastic gets scratched easily and can get hazy over time which reduces visibility when driving. It is for this reason that glass is the preferred primary material for making windscreens.

It is. There is a layer of plastic between 2 thin layers of glass in order to keep it from braking like normal window glass. Its not used for the outer layer because there does not exist a hard enough plastic that will not scratch after years of use like the glass windscreen. Just the action of the wipers would turn the plastic screen into a hazy mess in no time.

Scratches too easily. Bit of dirt or bird poo under the wiper blade and your plastic windscreen will be ruined.

Plastic is used, a layer of plastic between two layers of glass.

It scratches. I use it on my old 1948 jeep. glass cracks when I fold windshield down so I went to a polycarbinate. I have to replace it every few years when it gets scratched up.

The surface of Lexan and Plexiglass is too soft! It would abrade and scratch up too easily. Look at a plastic head-lamp on a 10 year old car. You couldn't see through it!

Vehicle windshields or windscreens are made of multiple layers. One of the layers is plastic.