Why are cirrus clouds more common on Mars? Mars water  ice clouds are often associated with regional- 
  to-global circulation and saturation conditions, as opposed to local convective overturning, and so typically exhibit cirrus rather than cumulus forms.


Source: The Atmosphere and Climate of Mars Edited by  Robert M. Haberle et al., 2017 - chapter 5 - subchapter 5.2

Why are cirrus clouds more common than cumulus clouds on mars?
Hmm... here's my guess.
Cumulus clouds form due to warm, moist air rising. With the atmosphere of Mars being so cold, there's little heat to facilitate the formation of cumulus clouds. Cirrus clouds, on the other hand, are composed of sparse ice crystals, which makes them probably more common on Mars than cumulus clouds. After all, supercooled water does become ice.