New planes? They are indeed luxurious, with panels that make a modern car look simple. Have you seen the multipanel displays that are going in? The instrument panel alone is worth more than a new car. A car can be assembled on an assembly line in about a day, yes? With components all trucked in from here & there feeding an assembly line. Planes don't sell in that kind of quantity.
Look at the data here:
As of 2019, there are more than 446,000 general aviation aircraft in the worldwide fleet, ranging from small training aircraft and helicopters to intercontinental business jets. About 213,000 of these, or 48%, are based in the United States. There are more than 5,000 public airports in the U.S. vs. fewer than 400 airports served by commercial airlines.
2019 Worldwide plane deliveries: 2,443.
Can manufacuturers dwarf that number.
Toyota’s motor vehicle production reached almost nine million units in the fiscal year ended March 31, 2019.
And that's just 1 manufacturer. VW, GM, Ford, they're all huge.
Another factor: Just about anyone can get a drivers license and drive a car, with many multi-car households. It takes a fair bit of dedication to get a pilots license, months of training, and then ongoing practice and a minimum of bi-annual recurrency testing/training to keep that license, along with keeping somewhat medically fit. And then supplies like charts that are updated every 6 months, down to 2 weeks for approach plates. When's the last time you updated a car map? I only use the GPS moving map in my car.
Older planes can be retrofitted with the latest and greatest avionics, with equipment costing more than a new car (example, a new Avidyne IFD550 GPS/NAV/COM can be over $15K USD - plus installation).
An engine flown for 100 hours a year can last 20 years, and then it can be overhauled, or replaced for $50K or more.
Planes get inspected annually, and much more thoroughly than the inspection a state may impose on car owners for 39 a year. Some states there is no inspection at all.
Aluminum planes can be repainted, a thorough process where by everything that can be removed is, and all the bits cleaned & repainted individually, then reassembled. A paint job can cost the same as buying a small car. Repainting a car by comparison is dirt cheap and is done in a few days,
Vs 6-8 weeks for an airplane for disassembly, prep for stripping, cleanup where stripping missing, alodyne to treat the aluminim, primer, finally paint, and then reassembly. Composite planes, I don't know the process.
Operating: planes use a lot more fuel per hour to cover ground a lot faster.
Say you had a 180 HP plane burning 10 gal/hr and going 125 mph ground speed (into some headwind).
To go 300 miles will take about 2.4 hours, 24 gallons of gas at roughly 5/gallon = 120.
A car might average 60 miles/hr, taking 5 hours, and getting 30 mpg, so 300 miles = 10 gallons @ 3/gallon, so 30 in gas.
That 300 mile road distance is almost always fewer air miles.
Example, it is 183 nautical miles (210 statute miles) to fly from my home airport to Bangor, Maine, a trip I am making in the next month or two.
1 hour, 26 minute flight. ~15 gallons of fuel $75.
Driving, 245 miles. 3 hour, 44 minute flight. $25 in fuel plus tolls.
Longer if there are construction delays (and it is summer construction season where I am) or traffic delays from accidents.
The time savings: 2 hours and 18 minutes. What's your time worth? $50/hr? So $115 saved by flying. Makes up for the difference in fuel cost.
Am I taking my 1973 plane with new paint job and avionics? Or my 2016 car with moving map? The plane for sure.