That's not 'only'. Nothing much can withstand sand. Diamond, possibly. Sand can quickly and easily scratch _anything_. I used to be a bicycle mechanic for competion racers, and expensive, high-quality, super-hard bearings could be quickly (as in one, short, trip) scratched by sand even though you couldn't make a notch in it with anything in the toolbox.

Put a piece of glass in a pocket, a mirror for example, with some sand grains. Walk around. See what happens.

The only thing that helps against sand is to let it scratch something else, i.e. a screen protector that you then replace.