In my hometown, they throw so much salt on the roads, this kills everything metal, even aluminum.

So people have winter beater bikes and winter beater cars.

Not sure what they do over there where you are, but corrosion causes are always the same: water infiltration.

You can try your best with preventive measures like loads of grease/lube/inhibitors, wash the bike after each ride, and despite all that it still happens.

You got it easy. Should see what this does to some new ebikes are 1 winter as well.