They do on some cars. On the Grand Caravan they have a small grid that goes across where the wipers lay and my 1989 Taurus had the full Insta-clear windshield that had a transparent copper tint across the whole thing that acted like a defroster. Push the button and watch the snow and ice melt!
Problem was how expensive it was if you needed to replace the windshield. At $900 for a replacement after a rock chip, it didn't take long for folks to stop buying the option.
It was great when it was new though. Now they have supplemental electric heaters in the defrost so you don't have to wait for the engine to warm up to clear the windshield. My 300 C has it and the ice starts melting in about 3 minutes. I hit the remote start when I'm upstairs putting my shoes on and by the time I get downstairs, grab my stuff and go out to the car, the windshield is melting the ice, the seats are warm with the seat heaters and the steering wheel is toasty with the wheel heater.