Due to a combination of public liability concerns and a driving public who are a liability, they put so much salt down on our roads during the cold months, now with 'pre-wetting'. That's with added water injection from tanks strapped to each side of the gritter to make the salt melt (and therefore coat your bike) quicker! Road salt then also stays 'in' the road surface for most of the year. What chance all these clever coatings?
The only protection is to wash your bike after every run and keep it liberally coated with anti corrosion spray.