Why is ice on Mars not covered in dust? There's exposed water ice on Mars, like in craters like this

At the same time, Mars has dust storm, covering the solar panels of rovers, and occasionally covering the entire planet

So why is this ice not covered in dust?

I understand that dry carbon dioxide ice can maintain a clean surface, as it's seasonally sublimated into the atmosphere and re-deposited, but how come water ice (at least some of it) is also left clean?
A lot of the water ice on mars is covered with dust.  NASA's Phoenix mars lander only had to scrape off some of it to find the layer of ice underneath  as seen here: https://www.nasa.gov/mission_pages/phoenix/images/press/sol_020_024_change_dodo_v3.html