What the sibling said about noise and vibration, plus the fact that you are in the seat for less time (the rest of the time spent in airports, walking from point to point, standing in line, etc.), plus the fact that you can get up and walk around at any time (I always get aisle seats).

Yes, at least for me, it's not just the size, it's also the vibration. And while the noise is usually louder in the plane, its nature is somehow worse in the car.

Probably because jet engines operate smoothly at constant RPM so the sound is monotonous and gets tuned out quickly, whereas car engines operate roughly at low and wildly varying RPMs. It also depends on the car--a Toyota Yaris with a 4 speed auto (lol in 2016) would pretty awful, where as a Lexus LS600h with V8 and CVT would be very pleasant.