Those are the only two states I've lived in. I don't get why so much of the country doesn't do these; it seems the Northeast of the US almost all require periodic safety inspections and the western US does not.
Missouri's inspection is on par with CT and VA from my experience. But that's the only midwest state I have lived in.
If I had a hunch, income plays a part. Flyover states are poor, that means older and more beat up cars. Older cars (out of warranty let's say) are more costly to fix. States have to balance "people need a car to make money" with "people need money to drive safe cars".
At least where I have lived if there is an emissions check it is a separate test. I think the inspections I have had to do involve brakes, lights, steering/tie rod, windows (no cracks/chips), exhaust, and I think in VA the engine light could only be on for frivolous things.
