"We have right now 1.3 billion cars (that are) internal combustion engine powered on the planet. We need to replace that with clean mobility" Why do we need to

"We have right now 1.3 billion cars (that are) internal combustion engine powered on the planet. We need to replace that with clean mobility" Why do we need to replace 1.3 billion engines instead of reducing the need for having them in the first place? What if we reduce mobility by say 20%? Not only less cars of any kind but less infrastructure to build and maintain.