High humidity will always do it over time.
Picture this: In an area with high humidity, walk outside with a hot cup of coffee & a glass of ice cold water. Out side of glass immediately gets wet, outside of coffee cup stays dry. Humid warm air condenses on cooler surfaces, not on warm surfaces. Temperature of metal points drops at night, warmer air on following day condenses on the cooler metal point surfaces promoting oxidation.
Even though expensive, in an enclosed garage, one remedy is to place a dehumidifier in the garage. In arid regions, with dry air, this is not a problem.
Point file is the one of the best tools for removing this mild insulating corrosion on points -- it removes mild corrosion, but not much metal, & leaves no grit residue from sandpaper.