Your data point is incorrect, but I’ll use it.
A $30,000 car that is 20 years old is a $500 car. People who drive $500 cars are one of the following:
A. Unable to afford a more reliable, more capable car, in which case a usage-based autonomous vehicle fleet model would be a better investment. It’s a direct cost for usage of state-of-the-art product, rather than a bulk gamble on an outdated product that deteriorates and requires maintenance and repair over its lifetime. I cannot overstate the real-world impact of that gamble: while on paper, it may sound like dropping $1,200 for a new transmission pans out to a few hundred dollars extra per year of vehicle ownership, the people who can’t afford a more reliable car are also unlikely to have the means to foot a $1,200 repair bill, which means their choices are to a) take out a loan (which, for these folks, usually equates to astronomical interest rates), or b) not go to work. Did I mention they probably work for an hourly wage, so they’ve been hemorrhaging income from the moment the car broke down? A $1,200 repair bill to this economic demographic often creates significant hardship for months, if not longer. It’s a financial snowball effect that can ruin someone, and by design, would not happen if transportation were usage-based.
B. Not interested in making a serious investment in a car as a status symbol or source of material satisfaction, in which case the autonomous fleet model is again a better investment.
C. Ready to soon enter the market for a new vehicle, which negates your argument.
As far as the “1/4” of people driving newer cars, there are many market factors which disrupt conventional logic. For one, 3/4 of people riding around in exponentially-safer autonomous vehicles leaves the human-piloted 1/4 paying deservedly exorbitant insurance premiums, since they are to AVs what drunk drivers are to conventional traffic. So your brand-new $30,000 car doesn’t seem worth much lined up against a $5,000 annual insurance premium.
That’s the rational side. The irrational side, which you can study in many a best-selling book or course on economics, says that people will also make the shift regardless of whether it solves a real need or makes financial sense. I just wrote an entire article showcasing consistent proof of that behavior.