You really can keep a car its whole life without selling it. I know a lot of people who have cars for 20 years or more and make out just fine. And that's in a world where cars get better, which isn't a concern in the NBA. Newer cars are inherently better than older cars, but newer players aren't necessarily better than older ones.
The point is that no one really cares about "value" except for folks like Morey and Hinkie. Like sure, if you're going to trade him, you want the most you think you can get. But what determines if you trade someone isn't how much they're worth. That's bull moneyball logic that doesn't work in a sport where team dynamics matter. DeRozan is a person, not just an "asset". His value is in what he can give, not in what he'd go for on EBay. Teams that win the trade war rarely win anything of consequence on the court. SA has long not been that kind of team, and their record speaks for itself.