As others have said, it comes down the coating, your finger's cleanliness, as well as, those keys listed in the Reddit article are lettered. I imagine the lettering process makes it thinner in that area, which makes any oils, debris etc... have an easier time penetrating the area of the letters, as seems to be witnessed in the pictures.
I plan on doing zinc alphas, but of the blank variety, to help mitigate any potential issues with wear, on top of maintaining clean hands and the like.