This object is actually big enough to have its own micro-gravity.
Ice that is moved around will, over time, do what water and glaciers do. It will flow, and fill up small holes.
Don't forget that it is a comet, and occasionally approaches the sun, a significant source of warmth.
I don't think I'm the one who is forgetting anything.
No one has explained how you can get round craters in a field of ice. Melting/evaporation makes craters even more unlikely.
ML/NJ