In any case, something makes cars depreciate over time. Lots of people don't dump their cars just because they're tired of them. And, if you're just driving somewhere like the US Southwest, age probably isn't the issue.
Some of these cabs are lasting 30+ years, though they often use old cop cars which also have high mileage. The limitation is offen accidents not direct mileage.
In any case, something makes cars depreciate over time. Lots of people don't dump their cars just because they're tired of them. And, if you're just driving somewhere like the US Southwest, age probably isn't the issue.