Car: acoustic treatment + 4 sides of HUGE GLASS windows + sound dampening + Engine NOISE + Wind NOISE + Tire/Road Noise = lots of noise and sound reflection.
Home: DEAD SILENT + acoustic treatment = ZERO NOISE and little sound reflection.
How MANY cars actually have enough sound proofing and acoustic treatment to rival home environment with acoustic treatment and zero noise floor?
How many people can afford cars that are the quietest with a cabin noise of 58dBA?
My wife's $32K Honda Odyssey is 70dB at PARK. It's probably 75dB @ 60 MPH.
My $92K Lexus LX570 isn't dead silent at park either. I'm guessing it's probably around 58-60dB.
You don't need 4 Oscars to figure it out.
The quietest car has a cabin noise of 58dBA @ 60 miles per hour.
http://elevatingsound.com/the-top-30-quietest-cars-a-cabin-noise-test-by-auto-bild/
Even if you soundproof the car, the noise would still be in the 50s.
In a treated home environment, the noise floor is dead silent (perceived).