I read through the report linked above, it basically comes down to too much of a safety trade off using a salt alternative.

People generally don’t care much for their cars, and the damage to infrastructure and environment is seen as fixable after the fact. Essentially, the death and injury/accident rate would increase under a salt alternative, which is seen as less favorable compared to preserving bridges and the environment.

So if there is to be a salt alternative, it would need to be almost nearly as effective if not better than salt would be right now.