It's about the money.

The smog business generates a ton of money.
It keeps people going back to the dealed.
Smog certificates puts money in the states pockets.

A stock 55 Chevy puts out less smog than a newer smog car.
If the goverment was serious about smog it would, Time stop lights in town to keep trafic flowing.
Limit jet aircraft landings at airports. They burn a ton of fuel on take off.
And diesel would be the most popular fuel.

Again it's about the money, not common sence.