If somebody compromised a car ECM why would they do anything as childish as running a botnet or mining bitcoin? If they just make every car of a specific model

If somebody compromised a car ECM why would they do anything as childish as running a botnet or mining bitcoin? If they just make every car of a specific model engage their ABS system to disable the brakes and set the cruise control to 200 km/hr at rush hour they could easily kill tens of thousands of people in a minute without giving any warning or leaving any ability to respond which would completely destroy any car manufacturer in an afternoon. They could literally blackmail billions of dollars from any car manufacturer instead of mining bitcoin for pocket change.