Yeah, same for all the drug kingpins with their "US dollars"

given the amount of regulatory gates you must pass through to purchase a car (license, registration etc), I doubt that criminals are going to use Bitcoin payments for criminal services to purchase a car.

They are far more likely to convert to fiat currency and then purchase the car.

Mixers are not that effective these days.

How not? Can you point some research in this direction?

There are companies, such as Chainalysis that specialize in analyzing the graph created by mixers/tumblers. If you want a coin that truly cannot have it's origins traced, use Monero, since it's a completely different structure with a public/private "view" key. It's actually a very interesting system.