The handling of those huge Auto Union rear-engine racers was so…unconventional…that the company began hiring motorcycle racers who had never driven a car as their race drivers. The oversteer of those cars was so treacherous that most people who had learned to drive on front-engine cars just couldn’t seem to learn how to deal with that oversteer.
After they switched to using motorcycle racers, the death toll from those cars did drop to a considerable extent. When I was a teenager, I read the autobiography of Rudolf Carracciola, who drove for Mercedes and at least one other manufacturer (possibly Alfa-Romeo?) during the '30s, and I learned a lot about those Auto Union racers from his book. Carracciola considered the AU cars to be…scary.