There are other problems
Pollution from cars is only one of the world's problems. Most of them are created by people and the need to consume. The only solution is less people; anything else is just a temporary fix. Even less people will not fully solve the problems, just slow them down...the world as we know it will not last forever, sooner or later there will be no humans. Does it matter if the end is in 200 years or 200,000 years?