Just a guess: The weaker gravity (around 1/3 of Earth's gravity) makes it much easier for wind to pick dust off the ground. Once a dust storm starts, it would also take a lot longer for the cloud of dust to dissipate.

Look at the videos of astronauts on the moon from the Apollo landings. Everything they do kicks up a significant amount of dust that takes quite a while to dissipate. Obviously it's not a perfect comparison because the moon has weaker gravity and a different composition.

Apparently the small amount of atmosphere means most of the wind is caused by changes of temperature from sun-heat. The atmosphere heats up very quickly over large areas. I imagine that an area the size of several countries going from -50 to +50 in a couple of hours could raise up some dust, no matter how thin the atmosphere...