What kind of decades worth of data are you referring to that will be beneficial to BMW et al in surpassing other competitors in this particular realm?
And while I agree with the sentiment of rather trusting a autonomous BMW with my life, I probably do it for different reasons. Assuming the worst, a heavy accident, I would want to be in a vehicle made by people that have more experience in designing cars to ace the crash tests. For now at least. That is a bit of experience I grant to the established brands.
But that is a sentimental, not a logical preference. Because whatever advantage BMW et al might have there can be matched by newcomers relatively quick. It's just mechanical engineering, not black magic. And the more digitally refined autonomous cars might have prevented the accident or softened the impact with an earlier reaction time in the first place.
Full disclosure: I love cars, I drive a BMW, I love it to death and will very likely keep it until it falls to pieces while other cars do the daily driving, but the attitude of the big brands towards the paradigm shift in mobility bugs me a lot.