As noted above, the mass to pass modern crash standards hurts mileage, as does emissions controls past a rational point.Honda CRX cars that still get 45-50 mpg without the hybrid stuff and the hybrids double cost.
To be clear on that last, lean burn, direct injection, etc. all have their effect on fuel economy, and emissions. If you pick a certain point in the cycle of smog controls, declare it good enough, and don't mind light cars that won't take what they will today in a crash, then you could indeed have 80+ mpg small cars, but not much better than 40 mpg for vans and heavy haul trucks. AND have pretty good smog control. The problem with regulation is there is no end. The people involved have jobs that depend on a continuous flow of work, and the work is making stricter rules. At some point in the 20th century, smog control was "good enough" to not kill that many people in an inversion in LA. ( some are going to die from pollen... let that be a Popular Panic and there would be Yard Police spraying Agent Orange on any flowers... )
OTOH, the regulations have brought us better fuel injection and traction control, and a 21st century Impala that you can ram a 1968 model head on and walk away. ( if you are in the New one ) The cost for that is high. Cars cost what houses did when I was a kid.
And I'd agree on the Hybrid cost thing, except it was less to get the Hybrid Rav-4 than to get a bigger infotainment screen package, about $800 price hike.
I AM well aware that the Nickel in my battery and the Rare Earths in my motors are Dirty Nasty stuff in mining and processing, and the costs are hidden by tax incentives, so you all are paying a tiny part of my bill. Thanks.
AND, my previous mileage machine was a VW diesel, and we know what happened there.... But it was a great handling car that got 40 mpg at 70 mph on the highway. ( and was MUCH heavier and newer than the really nice CRX )
It's funny... I had several motorcycles, from sub 400 cc, to 1100cc, 2 stroke and 4 stoke, and they all got the same MPG. About 35. Aerodynamics were lousy on all of them. But my current bike, a 1205cc torque beast, uses a very hopped up version ( 100 hp vs. 50 hp ) of a Harley Sportster engine. and it gets great mileage when cruising, about 55 mpg. Which proves that an engine with improved breathing and power potential gives better efficiency when run mellow.
Another funny thing is I can sell you a Mileage Gizmo that is just a hollow piece of plastic you put in a car's fuel line, and tell you that it improves your mileage by 3-4 mpg, and it will work, because you will drive different. You might even be angry that your wife, who doesn't know you spent time and money on it, won't get any different mileage because her habits don't change.