They were starting to inconvenience the wrong people. Kid gets pulled over while driving Dad's 450SL with some serious drugs, and they impound the car and sell it? The privileged won't put up with that shit forever, what's next, kid gets busted in the home and the cops seize the home?
It's not theft, it's blackmail. Most people won't fight hard to recover property taken during a drug bust or other crime, even if not related, because they want to avoid the legal system and cultural penalty for being involved with the police.
Is it worth it to spend the $10k you need to even start to fight the system to get a $50k car? You may be $50k into the fight before the cops have to even go to court to testify.