You've got it - "informed consent" is what's missing, some demonstration that what the drivers anticipated (and agreed not to claim against) was the only threat. The moment anything else appears contributory, the consent can be successfully attacked.

What killed the tobacco companies: even though it was known that smoking was dangerous 100 years ago (remember? called "coffin nails" in WW1?), it was discovered that the tobacco companies knew about and withheld even worse information.
This is the essence of fraud (and dealing in bad faith): the statements were known to be false, offered for the specific purpose of attracting new smokers, and the potential customers had no access to better information (called "substantial reliance").

It doesn't have to rise to the level of provable fact, only to the point where the defendant/respondent (insurance etc.) would rather pay than risk a big jury verdict.