Exactly the same reason things like Hillary or Obama's health care plan are impossible.
You are all smart enough to understand charging everyone the same for internet under the assumption most people won't use it is a stupid idea.
So why doesn't everyone understand charging people the same price for insurance under the assumption most people won't use it is also a stupid idea?
As with all things, you should pay for what you use. You shouldn't pay for what others use, and you shouldn't use more than you pay for.